The cross-section of a ventilation pipe is a square with sides 0.4 meters long and 2.5 meters long. If iron sheets are used to make 20 ventilation pipes like this, how many square meters of iron sheets are needed?
一个通风管的横截面是边长0.4米的正方形，长2.5米．如果用铁皮做这样的通风管20个，需要多少平方米的铁皮？
<gadget id="calculator">0.4 * 4 * 2.5 * 20</gadget>
<output>80</output>

<result>80</result>