Question

use a pronoun to avoid repeating words, if possible.
eleanor shellstrop and the librarian said that the used books were eleanor shellstrop and the librarians to add to the collection.

Explanation:

The task is to replace the repeated noun phrase "Eleanor Shellstrop and the librarian's" with a suitable possessive pronoun to avoid repetition. Since the phrase refers to two people (a plural group), the correct plural possessive pronoun is "their".

Answer:

Eleanor Shellstrop and the librarian said that the used books were theirs to add to the collection.