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 = 
<gadget id="calculator">4*3</gadget>
<output>12</output>
12 cups.
Carl sold 7 x 3 = 
<gadget id="calculator">7*3</gadget>
<output>21</output>
21 cups.
Carl sold 21 - 12 = 
<gadget id="calculator">21-12</gadget>
<output>9</output>
9 cups more than Stanley.

<result>9</result>