Ruel has four books of 10 stamps and six books of 15 stamps. How many stamps does Ruel have?
Ruel has a total of 4 x 10 = <T>multiply(4, 10)=40 stamps from the four books.
He also has 6 x 15 = <T>multiply(6, 15)=90 stamps from the six books.
Therefore, he has a total of 40 + 90 = <T>add(40, 90)=130 stamps.
