A metal ventilation pipe is 24m long and 0.2m in diameter. If such a ventilating pipe is made with 40 knots, how many square meters of iron sheets are needed at least?
一节铁皮通风管长24m，直径是0.2m．如果做这样的通风管40节，至少需要铁皮多少平方米？
<gadget id="calculator">3.14 * 0.2 * 24</gadget>
<output>15.072</output>

<gadget id="calculator">15.072 * 40</gadget>
<output>602.88</output>

<result>602.88</result>