A cylindrical swimming pool with a bottom diameter of 40 meters and 180 cubic meters of water per hour, how long does it take to make the water depth reach 1.8 meters?
一个圆柱形游泳池，底面直径40米，每小时放水180立方米，经过多少时间才能使水深达到1.8米．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

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

<gadget id="calculator">1.8 / 180</gadget>
<output>0.01</output>

<gadget id="calculator">3.14 * 400 * 0.01</gadget>
<output>12.56</output>

<result>12.56</result>