Paul had w books. After giving x books to his friend and selling some books in a garage sale he had y books left. How many books did he sell in the garage sale?
Paul had 134 books. 

After giving 39 books to his friend, he had 95 books left. 

After selling some books in a garage sale, he had 68 books left. 

So, he sold 95 - 68 = 27 books in the garage sale.