Question

Change the voice

3) Post the letter.​

Answer 1

Answer:

Let the letter be posted.

It is imperative sentence so it is your answer.

I also say you the rule: Let+Subject+be+V3

I also suggest you that here "the letter" is subject so I should not use "You are ordered to".Hope it will help you.

Answer 2

the given sentence is an Imperative sentence

Imperative sentence is a sentence used to give command,instructions,requests..etc;

we can convert an imperative sentence into passive by using any of the following structures:

Let this letter be posted.

This letter must be posted.

This Letter should be posted.

You are ordered to post this letter.