For a pile of coal, 20% of the total amount is removed for the first time, and (2/5) of the total amount is removed for the second time, exactly 90 tons. How many tons does this pile of coal have?
一堆煤，第一次运走总数的20%，第二次运走总数的(2/5)，正好运走90吨，这堆煤有多少吨？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) + (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">90 / (3/5)</gadget>
<output>150</output>

<result>150</result>