How many square decimeters of iron sheet is required to make a cylindrical iron ventilation pipe with a bottom diameter of 4 decimeters and a height of 5 decimeters?
做一个底面直径4分米，高5分米的圆柱铁皮通风管，需铁皮多少平方分米．
<gadget id="calculator">3.14 * 4 * 5</gadget>
<output>62.8</output>

<result>62.8</result>