Answer:
21 shelves
Step-by-step explanation:
I'm going to guess that you want to know if Kevin is correct in his estimate.
How many books are there is total?
12 boxes * 31 books/box = 372 books in total
Each shelf will hold 18 books so
372 books * [1 shelf /18 books] = 20.6666 shelves.
To be safe unless he wants to stake some of the left over books, he will need 21 shelves. You have to round up for the left over books. 20 shelves is a good estimate, but you will need just one more that has 1/3 of a shelf left over. He can put a picture of his family there.
