Title: There are the same number of books in the corner of Class One and Class Two in Grade Four. If you take out 30 books from 1 class and 12 books from class 2, the number of books in the corner of class 2 is four times that of 1 class. How many books are there in the corner of Class One and Class Two?

Solution: Suppose there are X books in the corner of Class One and Class Two.

x- 12=(x-30)×4

x- 12=4x- 120

4x-x=- 12+ 120

3x= 108

x= 108÷3

x=36

There used to be 36 books in the book corner of Class One and Class Two.