Help me with school book problem!?

-So, I took chemistry this year, but dropped the course because it messed up my schedule. I gave my friend my book and told him to return it to her, and he says he did. But today I got a letter in the mail saying I owe the teacher my book, when I don't have it because I gave it to my friend to return to her, and my friend isn't a liar, because he says he did return it. The book is $60, and I don't know what to do. My mom and dad will be angry if they have to pay for a book I returned. What should I do? Schools out so I cannot physically go there and see the teacher. I don't know her email address, and I refuse to pay for a book I returned!! Please help!are you sure he returned it? maybe he lost it, or didn't tell the teacher it was YOUR book. So she just marked it as lost and returned or some crap. Talk to your friend again, mare SURE!!!! Sorry if you have to pay for it. But its your fault, you shouldn't trust anyone, even your friends. You should have done it yourself.
You can find the book online for cheaper and buy another copy.