To make a water pipe with a bottom diameter of 8 cm and a length of 10 cm, at least how much iron sheet is needed.
做一节底面直径是8厘米，长10厘米的水管，至少需要铁皮多少．
<gadget id="calculator">3.14 * 8 * 10</gadget>
<output>251.2</output>

<result>251.2</result>