There are w different movies and x different books in the ' crazy silly school ' series. If you read y of the books and watched z of the movies How many more books do you still have to read?
There are w different movies and x different books in the ' crazy silly school ' series. If you read y of the books and watched z of the movies How many more books do you still have to read?

You have read 4 books and watched 34 movies. 

You still have to read (x - y) books. 

You still have to read (19 - 4) books. 

You still have to read 15 books.