A pile of coal, 30% is used for the first time, 45% is used for the second time, and 4.5 tons more is used for the second time than the first time. How many tons is this pile of coal? (column equation solution)
一堆煤，第一次用去30%，第二次用去45%，第二次比第一次多用4.5吨，这堆煤有几吨？(列方程解答)
<gadget id="calculator">4.5 / 0.15</gadget>
<output>30</output>

<result>30</result>