Question

he sent a letter to the customer active voice to passive voice​

Answer 1

Answer:

The sentence represents ‘past indefinite tense or simple past’

Its passive form should be- (was/were+V3) The object of the sentence(active voice) that is ‘a letter’ would be changed as subject in it’s passive form.

So the answer is-

A letter was sent to the customer by him.

We can remove ‘by him’, as it is not important to use the ‘Agent’ here because one should use ‘Agent’ only if it is required to clarify the meaning of the sentence. So it would also be right if you write-

A letter was sent to the customer.

Explanation:

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Answer 2

Answer:

A letter being sent by him to the costomer.