NOTE: I am self studying UML so I have nobody to verify my diagrams and hence I am posting here, so please bear with me. This is the problem I got from some PDF available on Google that simply had the following problem statement:

Problem Statement: A library contains books and journals. The task is to develop a computer system for borrowing books. In order to borrow a book the borrower must be a member of the library. There is a limit on the number of books that can be borrowed by each member of the library. The library may have several copies of a given book. It is possible to reserve a book. Some books are for short term loans only. Other books may be borrowed for 3 weeks. Users can extend the loans. Draw a use case diagram for a library.

I already drew the Use Case diagram and had it checked by a community member. This time I drew sequence diagrams for borrowing a book and extending the date of return.
Please let me know if they are correct.
I drew them using Visual Paradigm and I dont know how to keep a control of the sequence numbers. If you do, please let me know :)

Diagrams