pile of coal burns an average of 2.5 tons per day, and 6.7 tons remain after 7 days. How many tons does this ton of coal have?
一堆煤，平均每天烧掉2.5吨，7天后还剩6.7吨，这吨煤原有多少吨？
<gadget id="calculator">2.5 * 7</gadget>
<output>17.5</output>

<gadget id="calculator">17.5 + 6.7</gadget>
<output>24.2</output>

<result>24.2</result>