The school library has 140 comic books and 100 story books. Lend out four books every day. How many days later, the rest of the comic books are story books?
Comic books are more than story books 140- 100 = 40 (books). When comic books are three times as many as story books, they are 3- 1 = 2 times more than story books. At this time, how many days are there in the storybook (18)?