posted by Ray .
There are 25 books in a bookcase. The books in the bookcase are all math, science, and history books. Seven of the books are math books. There are 4 fewer science books than history books. How many science books are in the bookcase?
First you need to assign your unknowns
Math Books: 7
Science Books: x-4
Total books: 25
so your equation is going to be
Then you can solve. I hope this help!