How many square meters of iron sheet is needed to make a ventilation pipe with a length of 4 meters and a cross-section of a circle with a diameter of 12 centimeters.
制作一个通风管，长4米，横截面是直径12厘米的圆，需要多少平方米的铁皮．
<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">3.14 * (3/25) * 4</gadget>
<output>1.5072</output>

<result>1.5072</result>