To make a chimney with a bottom diameter of 20 cm and a length of 180 cm, at least how many square decimeters of iron sheet are needed.
做一节底面直径为20厘米，长180厘米的烟囱，至少需要多少平方分米铁皮．
<gadget id="calculator">180 / 100</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">3.14 * 20 * (9/5)</gadget>
<output>113.04</output>

<result>113.04</result>