A cuboid oil drum is filled with oil, poured out (2/5), and there are 30 liters left, the height of the oil drum is known to be (25/4) decimeters. What is the area of the bottom of the barrel?
一个长方体油桶装满了油，倒出(2/5)，还剩下30升，已知油桶高(25/4)分米．这个油桶的底面积是多少？
<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">25 / 4</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">30 / (3/5) / (25/4)</gadget>
<output>8</output>

<result>8</result>