To make a cylindrical ventilation pipe with a height of 20 cm and a bottom diameter of 12 cm, at least how many square centimeters of iron sheet is needed.
要做一个高20厘米，底面直径是12厘米的圆柱形通风管，至少需要多少平方厘米的铁皮．
<gadget id="calculator">3.14 * 12 * 20</gadget>
<output>753.6</output>

<result>753.6</result>