Answer:
13
Step-by-step explanation:
First, to find out how many book fit on one shelf, you will need to divide the total number of books by the toal number of shelves:
36 books / 3 shelves = 12 books/shelf
Because the question says that the bookstore order <em>another</em> 120 copies, this is means that the 120 books is in addition to the original 36 books.
Because we already know that the 36 books require 3 shelves, we still need to find how many shelves 120 books needs. So, we can divide books by number of how many books <em>can</em> fit on a shelf:
120 books / 12 books per shelf = 10 shelves
So to find the total number of shelves needed, add the number of shelves together:
3 + 10 = 13 shelves