To make a ventilation pipe with a bottom radius of 10 cm and a length of 0.6 m, at least how many square centimeters of iron sheet is needed.
做一节底面半径为10厘米，长是0.6米的通风管，至少需要铁皮多少平方厘米．
<gadget id="calculator">0.6 * 100</gadget>
<output>60</output>

<gadget id="calculator">3.14 * 10 * 2 * 60</gadget>
<output>3_768</output>

<result>3_768</result>