John buys 20 candy bars.  His brother Dave pays for 6 of them.  If each candy bar costs $1.50, how much did John pay?
He paid for 20-6=
<gadget id="calculator">20-6</gadget>
<output>14</output>
14 candy bars.
So he paid 14*1.5=$
<gadget id="calculator">14*1.5</gadget>
<output>21</output>
21.

<result>21</result>