pile of goods is transported away (1/4) for the first time, and (2/5) of all the goods is transported for the second time, leaving 21 tons. How many tons is this pile of goods?
一堆货物第一次运走它的(1/4)，第二次运走全部货物的(2/5)，还剩下21吨，这堆货物有多少吨？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">21 / (7/20)</gadget>
<output>60</output>

<result>60</result>