Solutions
Here, the sentence is given in two parts.
Part (1): You must understand clearly that
Part (2): this is the last time I shall allow it
Part (1) has not object. So, we’ll use “it” as an introductory subject in passive voice. Now, the sentence uses a modal verb. The structures for active/passive voices for modal verbs are:
Active: Subject + modal verb + verb (Ist form) + object...
Passive: Object + modal verb + be + verb (IInd form) + by + subject...
The sentence in Part (2) is of simple future tense. Let us understand the structures for active/passive voices for such sentences.
Active: Subject + will/shall + verb (Ist form) + object...
Passive: Object+ will/shall + be + verb (IIIrd form) + by + subject...