cylindrical oil drum filled with gasoline. After pouring out (3/4) gasoline, there are 20 liters left. The area of the bottom of the barrel is 10 square decimeters. How tall is the barrel?
一个圆柱形油桶，装满汽油．倒出(3/4)的汽油后，还剩下20升．油桶的底面积是10平方分米．油桶的高是多少？
<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">20 / (1/4)</gadget>
<output>80</output>

<gadget id="calculator">80 / 10</gadget>
<output>8</output>

<result>8</result>