There are two piles of coal, pile A is 94 tons, pile B is 138 tons, and 9 tons are transported away each day. After how many days, the remaining coal in pile B is 3 times that of pile A.
有两堆煤，甲堆94吨，乙堆138吨，每天各运走9吨，经过多少天后乙堆剩下的煤是甲堆剩下的3倍．
<gadget id="calculator">94 * 3</gadget>
<output>282</output>

<gadget id="calculator">282 - 138</gadget>
<output>144</output>

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<gadget id="calculator">27 - 9</gadget>
<output>18</output>

<gadget id="calculator">144 / 18</gadget>
<output>8</output>

<result>8</result>