cylindrical wine barrel is filled with wine, and there are 12 liters left after pouring out 2/5. Given that the height of the barrel is 5 decimeters, what is the bottom area of the barrel?
一个圆柱形的酒桶，里面装满酒，倒出2/5后还剩12升．已知桶高5分米，求酒桶的底面积？
<gadget id="calculator">2 / 5</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">12 / (3/5) / 5</gadget>
<output>4</output>

<result>4</result>