A pile of coal, after burning (3/4), there are still 15 tons left. How many tons is this pile of coal?
一堆煤，烧去(3/4)后还剩下15吨，这堆煤有多少吨？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">15 / (1/4)</gadget>
<output>60</output>

<result>60</result>