A cylindrical water pipe has an outer diameter of 22 cm and an inner diameter of 20 cm. The flow rate of water in the pipe is 40 cm per second. How many cubic centimeters of water flow per second?
一根圆柱形水管，外直径22厘米，内直径20厘米，水在管内的流速是每秒40厘米，每秒流过的水是多少立方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100 * 40</gadget>
<output>12_560</output>

<result>12_560</result>