Question

my father will write a letter convert into passive voice

Answer 1

A letter will be written by my father.
Hope it helps.

Answer 2

Answer:

A letter will be written by my father

Explanation:

This is because there we need to swap the Subject and object

Father will become Letter

Letter will become Father

Then we need to add a helping verb and convert the main verb into V3 ( Past Participle)

In the end, add a preposition by to complete the sentence