By mistake, I ruined the library book. What is the penalty?
Talk to the campus library staff about the damage when you return the book. Library staff will assess the damage and decide on the fines. If the book is usable, there will be just a minimal penalty. If the book is beyond repair, you will be invoiced the price of the book as replacement cost, plus a $10 processing fee. This is done on a case-by-case basis.
Better to call the library ahead of time to discuss the situation.