The price of ribs this morning was 17.50 yuan per catty. My mother bought 2.4 catties of ribs. She paid the butcher 50 yuan. How much should I get back?
今天早上排骨价格是每斤17.50元，妈妈买了2.4斤排骨，她付给卖肉师傅50元钱，应找回多少钱？
<gadget id="calculator">2.4 * 17.5</gadget>
<output>42</output>

<gadget id="calculator">50 - 42</gadget>
<output>8</output>

<result>8</result>