Question

Type these letters at once change the voice

Answer 1

PASSIVE VOICE

These letter is typed at once.

Answer 2

Active voice coversion into a passive voice expression is really easy. However, we must follow the fundamental guidelines given in the grammar of a language.

Anyhow, in English, the change of place of the object and the subject is needed. But, when the object or subject is not illustrated in a statement, we need to insert one. Such is the case here.

Answer: "These letters must be typed by you at once." ("you" is inserted in the sentence).