[Grammar] "From which" vs "which"

[drps4]

I have question about following sentences.

1. Please return the book back to the library from which you have rented it.

Can this sentence be changed to this?

2. Please return the book back to the library which you have rented from.
3. Please return the book back to the library which you have rented it from.
4. Please return the book back to the library where you have rented it from.

My question is, when do I have to use "from which/in which/on which" in the sentence?

 

[Roman55]

I am not a teacher.

There are a couple of things wrong with your sentences, which have nothing to do with your question.

You 'return' a book, you don't 'return (it) back'.

We don't normally 'rent' books from libraries, we 'borrow' them.

So, I think 1. should have been, 'Please return the book to the library from which you borrowed it.'

Assuming you make those changes, I only like version 3.

The natural way of saying it for me would be, 'Please return the book to the library you borrowed it from.'