To make three cylindrical ventilation pipes with a base diameter of 12cm and a length of 20cm, at least how many cm**2 iron sheets should be used.
制三根底面直径12cm，长20cm的圆柱形通风管，至少要用多少cm**2的铁皮．
<gadget id="calculator">3.14 * 12 * 20 * 3</gadget>
<output>2_260.8</output>

<result>2_260.8</result>