To make a cylindrical ventilation pipe with 2 bottom diameters of 2dm and a length of 9dm, at least how much iron sheet is needed.
做2节底面直径是2dm，长9dm的圆柱形通风管，至少需要铁皮多少．
<gadget id="calculator">3.14 * 2 * 9 * 2</gadget>
<output>113.04</output>

<result>113.04</result>