There are 15 tons of steel in the warehouse. 20% of the total is used for the first time, and the rest (3/5) is used for the second time. How many tons of steel are left? (Only the column formula does not count)
仓库里有15吨钢材．第一次用去总数的20%，第二次用去剩下的(3/5)，还剩多少吨钢材？(只列式不计算)
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(4/5) * (1/5)</gadget>
<output>4/25 = around 0.16</output>

<gadget id="calculator">150 * (4/25)</gadget>
<output>24</output>

<result>24</result>