Each shelf of a bookcase contained 12 books. If the librarian took out 21 books and rearranged the remaining books so that all shelves but the last one contained 8 books and that last shelf contained 15 books, how many shelves does the bookcase have?
Pick one
A) 5	B) 6	C) 7	D) 8	E) 9
Let x be the number of shelves.   12x - 21 = 8(x-1) + 15   4x = 28   x= 7   The answer is 7.
<result>C</result>
Each shelf of a bookcase contained 12 books. If the librarian took out 21 books and rearranged the remaining books so that all shelves but the last one contained 8 books and that last shelf contained 15 books, how many shelves does the bookcase have?