Joy has 30 pencils, and Colleen has 50 pencils. If they bought the pencils at $4 each at the store, how much more money did Colleen pay than Joy for her pencils?
The number of pencils that Colleen has more than Joy is 50-30 = 
<gadget id="calculator">50-30</gadget>
<output>20</output>
20 pencils.
If each pencil was sold at $4 each, Colleen paid $4*20 = $
<gadget id="calculator">4*20</gadget>
<output>80</output>
80 more for the 20 extra pencils she has more than Joy.

<result>80</result>