The given sentence is in active voice. It uses a modal verb. The structure for active/passive voices for such sentences are:

Active: Subject + must/may/might/can +verb (Ist form) + object...

Passive: Object + must/may/might/can + be + verb (IIIrd form) + by + subject...

The passive voice of the given sentence would be:

This book must be read by everyone.

The given sentence is in active form of simple past tense. The structures for active/passive voices are:

Active: Subject + verb (IInd form) + object...

Passive: Object + was/were + verb (IIIrd form) + by + subject...

So, with the help of the above structures, we can convert the given sentence into passive voice:

It was known to him that his own life was unjust.

The given sentence is of present perfect tense and it is in active form. The structures for active/passive voices are:

Active : Subject + has/have + verb (IIIrd form) + object...

Passive: Object + has/have + been + verb (IIIrd form) + by + subject...

So, the passive voice of the given sentence would be:

The answer has been learnt by heart by the student.

The given sentence is in active form of simple past tense. The structures for active/passive voices are:

Active: Subject + verb (IInd form) + object...

Passive: Object + was/were + verb (IIIrd form) + by + subject...

So, with the help of the above structures, we can convert the given sentence into passive voice:

The cow was patted and touched by the old lady.

The given sentence is the passive voice of simple past tense. The structures for passive/active voices are:

Passive: Object + was/were + verb (IIIrd form) + by + subject...

Active: Subject + verb (IInd form) + object...

So, with the help of the above structures, we can convert the given sentence into active voice:

My grandfather gave me this watch.

The given sentence is in interrogative form. To convert such sentences into direct narration, the below rules are followed:

• Said/say is changed to ask/asked/wonder/wondered/enquire of/enquired of.
• Inverted commas (" ") are removed.
• If the reported speech is in YES/NO question form then if/whether is used before reported speech.
• If the reported speech is in the form of WH-Question (who/what/why/how/where/when/which etc), no conjunction is used before the question word. The question word itself works as a conjunction.
• Reported verb is made assertive; i.e. it is kept in the order of subject + verb.
• The sign of interrogation (?) is removed and full stop is used.
• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Since the question sentence starts with "may", we'll use "if/whether" in indirect sentennce as conjunction. "May" will change to "might"

Rules for changing the direct speech into indirect speech are given below:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and “that” conjunction is used.
• Says to/said to changes to tells/told in indirect speech if they are followed by an object. If not, they would remain same in indirect speech.

How to changes the tense in indirect speech

• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• Can, shall, will, may, must changes to could, should, would, might and must respectively.
• If there are any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.

How some words change in indirect speech

• Words like “this, these, tomorrow, yesterday change to that, those, the next day, the previous day” respectively.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

The sentence is given in indirect speech and we need to convert it into direct speech. While converting the sentence into direct speech, the conjunction "that" is replaced by inverted commas (" "). The tense of the reported speech is past continuous which will change to present continuous in direct speech. The word "next day" will change to "tomorrow". The pronoun "she" will change to "I" in direct speech. So, the direct narration of the given sentence would be:

Radha said, "I was going to Patna tomorrow."

The given sentence is the combination of affirmative and interrogative sentence. So, we'll use the rules of simple and interrogative sentences.
 

Rules for changing the direct speech into indirect speech:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and “that” conjunction is used.
• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• Can, shall, will, may, must changes to could, should, would, might and must respectively.
• If there are any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.
• Words like “this, these, tomorrow, yesterday change to that, those, the next day, the previous day” respectively

Rules for changing the direct speech into indirect speech for interrogative sentences:

• Said/say is changed to ask/asked/wonder/wondered/enquire of/enquired of.
• Inverted commas (" ") are removed.
• If the reported speech is in YES/NO question form then if/whether is used before reported speech.
• If the reported speech is in the form of WH-Question (who/what/why/how/where/when/which etc), no conjunction is used before the question word. The question word itself works as a conjunction.
• Reported verb is made assertive; i.e. it is kept in the order of subject + verb.
• The sign of interrogation (?) is removed and full stop is used.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

Rules for changing the direct speech into indirect speech are given below:

• The inverted commas (“ “) used in Direct Narration is removed in Indirect Narration and “that” conjunction is used.
• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech.
• If the reporting verb is in past tense, we make changes to the reported verb as per the below rule:
• Simple present tense changes to simple past tense.
• Present continuous tense changes to past continuous tense.
• Present perfect tense changes to past perfect tense.
• Present Perfect continuous tense changes to past perfect continuous tense.
• Simple past tense changes to past perfect tense.
• Past continuous tense changes to past perfect continuous tense.
• No changes are made to past perfect and past perfect continuous tense.
• Can, shall, will, may, must changes to could, should, would, might and must respectively.
• If there are any universal truth, habitual fact in the reporting speech, no changes are made to the reported verb’s tense.
• Words like “this, these, tomorrow, yesterday change to that, those, the next day, the previous day” respectively.

Below are the rules for changing the pronouns correctly:

• First person pronoun changes according to the subject of reporting speech.
• Second person pronoun changes according to the object of reporting speech.
• Third person pronoun does not change in indirect speech.

For the given sentence, "said" will remain same in indirect speech as it is not followed by any object. Inverted commas will be replaced by conjunction "that" and the pronoun will change as per the above rules.