There are 15 tons of steel in the warehouse, 20% of the total is used in the first hour, and 4 tons are used in the second hour. How many tons of steel are left?
仓库里有15吨钢材，第一小时用了总数的20%，第二小时用去4吨，还剩下多少吨钢材？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

<gadget id="calculator">15 - 3 - 4</gadget>
<output>8</output>

<result>8</result>