Make a ventilation pipe with a length of 4 meters and a diameter of 0.2 meters. At least how many square meters do you need to use tinplate?
用白铁皮做一根长4米的通风管，管口的直径是0.2米．至少需要用白铁皮多少平方米？
<gadget id="calculator">3.14 * 0.2 * 4</gadget>
<output>2.512</output>

<result>2.512</result>