Stanley sold 4 cups of lemonade an hour. His brother, Carl, sold 7 cups of lemonade an hour. How many more cups did Carl sell than Stanley in 3 hours?
Stanley sold 4 x 3 = <T>multiply(4, 3)=12 cups
Carl sold 7 x 3 = <T>multiply(7, 3)=21 cups
Carl sold 21 - 12 = <T>subtract(21, 12)=9 cups more than Stanley
