Teacher Zhang brought 50 yuan to buy prizes, and bought 18 prizes of 2.4 yuan. How much should I get back?
张老师带50元钱去买奖品，2.4元的奖品买了18份，应找回多少钱？
<gadget id="calculator">2.4 * 18</gadget>
<output>43.2</output>

<gadget id="calculator">50 - 43.2</gadget>
<output>6.8</output>

<result>6.8</result>