To make a cylindrical chimney with a bottom diameter of 15 cm and a length of 4 meters, at least how many square meters of iron sheets are needed. (interface not counted)
做一个底面直径15厘米，长4米的圆柱形烟囱，至少需要用多少平方米的铁皮．(接口处不计)
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">3.14 * (3/20) * 4</gadget>
<output>1.884</output>

<result>1.884</result>