求问涛涛30-15

Q15:

At a certain bookstore, the regular price of each book is 20 percent less than its list price.  If during a sale the price of each book at the store was 15 percent less than its regular price, then the price of a book during the sale was what percent less than its list price?

A.    30%

B.    32%

C.    35%

D.    38%

E.    40%

答案B

我怎么算不出呢？