There is a cylindrical bucket with a bottom diameter of 40 cm and a depth of 90 cm. Now pour the full water into another cuboid tank. After pouring, the tank is still empty (1/5). It is known that the inner bottom area of the cuboid tank is 47.1 square decimeters. What is the height of the inner wall of this tank in centimeters?
有一个圆柱形水桶，它的底面直径为40厘米，桶深为90厘米．现将盛满的水倒入另一个长方体的水槽中，倒入后水槽还空着(1/5)，已知长方体水槽内部底面积为47.1平方分米，这个水槽的内壁高是多少厘米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">47.1 * 100</gadget>
<output>4_710</output>

<gadget id="calculator">90 / (4/5) / 4_710</gadget>
<output>15/628 = around 0.023885</output>

<gadget id="calculator">3.14 * 400 * (15/628)</gadget>
<output>30</output>

<result>30</result>