Introduction:
The bill payment was changed to passive voice, and we need to describe when the bill was paid.

Answer:

1. Active Voice:
In the active voice, the sentence "When did you pay the bill?" indicates that the subject, "you," performed the action of paying the bill.

2. Passive Voice:
To convert the sentence into passive voice, we need to rearrange the sentence and make the object of the active voice sentence the subject of the passive voice sentence. The verb should be changed to its past participle form, and the subject of the active voice sentence should be placed after the verb.

Passive Voice:
When was the bill paid by you?

Explanation:
The original sentence "When did you pay the bill?" has been transformed into the passive voice sentence "When was the bill paid by you?" In the passive voice sentence, the subject "bill" becomes the object, and the object "you" becomes the subject. The verb "pay" changes to its past participle form "paid," and the preposition "by" is added to indicate the performer of the action.

Benefits of Using Passive Voice:
Using passive voice can have several benefits in certain situations:

- Emphasizing the object: Passive voice allows us to emphasize the object or the recipient of the action. In this case, the focus is on the bill being paid rather than the person who paid it.
- Concealing the performer: Passive voice can be used to conceal the performer of the action. If the identity of the person who paid the bill is not important or known, using passive voice can be useful.
- Formal writing: Passive voice is often used in formal writing, such as academic papers or reports, to maintain an objective tone and focus on the subject matter rather than the writer or the reader.

Conclusion:
The original sentence "When did you pay the bill?" was transformed into the passive voice sentence "When was the bill paid by you?" By using passive voice, the focus shifts from the person who paid the bill to the bill itself. Passive voice can have various benefits, such as emphasizing the object, concealing the performer, and maintaining a formal tone in writing.