For a pile of coal, the ratio of the number of tons transported to the total on the first day is 1:5, and after transporting 4 tons on the second day, exactly (1/3) of the total is transported in two days. How many tons is this pile of coal?
一堆煤，第一天运走的吨数与总数的比是1：5，第二天运走4吨后，两天正好运走了总数的(1/3)．这堆煤原有多少吨？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">4 / (2/15)</gadget>
<output>30</output>

<result>30</result>