To make a ventilation pipe with a bottom diameter of 20cm and a length of 60cm, at least how many cm of iron sheet is needed**2.
做一个底面直径20cm，长60cm的通风管，至少需要铁皮多少cm**2．
<gadget id="calculator">3.14 * 20 * 60</gadget>
<output>3_768</output>

<result>3_768</result>