To be sent or to sent

In this sentence, to be sent is the correct form. However, it is not necessary: "remit the sum to the"......is enough.

Anonymous How would I know if one is incorrect and the other is correct?

The grammatical voice - active or passive - makes all the difference. (English wouldn't be English if there were no exceptions!)
You should read the books [which/that are supposed] to be read by next week.
The books cannot read. They won't do the reading. Someone

Thank you. Very helpful.

You wrote:

You should read the books [which/that are supposed] to be read by next week.

Whenever I see this kind of sentence ( or some sentence that has a pattern similar to this), I feel what is ellipted has to be in the form of "what/that is and are" and what you seem to be have as the part left out (and thus optional) is "which/that are

AnonymousCould we have thopught the part left out to be this?

You should read the books [which/that are] to be read by next week.

Yes, but including supposed is more common, especially in spoken English. Leaving it out may make the sentence sound unnatural. Another example:
He was [supposed] to come yesterday, but for some re