The cross-section of a ventilation duct is a square with side length 0.4 m and length 2.5 m. If 50 such ventilating pipes are made of iron sheets, how many square meters of iron sheets are needed?
一个通风管的横截面是边长是0.4米的正方形，长2.5米．如果用铁皮做这样的通风管50只，需要多少平方米的铁皮？
<gadget id="calculator">0.4 * 4 * 2.5 * 50</gadget>
<output>200</output>

<result>200</result>