A cylindrical oil barrel is filled with half a barrel of oil, and then 40% is poured out, leaving 12 liters. If the bottom area of the oil barrel is 10 square decimeters, what is the height of the oil barrel?
一个圆柱形油桶，装入半桶油，再倒出40%，还剩12升，若油桶的底面积是10平方分米，则油桶高是多少？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">12 / (3/5) / (1/2) / 10</gadget>
<output>4</output>

<result>4</result>