Grass carp is 12 yuan per kilogram. Mom bought a 1.5kg grass carp and paid 20 yuan. How much should I get back?
草鱼每千克12元，妈妈买了一条1.5千克的草鱼，付出20元，应找回多少元．
<gadget id="calculator">12 * 1.5</gadget>
<output>18</output>

<gadget id="calculator">20 - 18</gadget>
<output>2</output>

<result>2</result>