ventilation pipe has a pipe length of 30 meters and the mouth of the pipe is a square with a side length of 5 decimeters. How many square meters of iron sheet is needed to make this ventilation pipe?
一个通风管的管道长30米，管口是边长5分米的正方形．做这个通风管至少要多少平方米铁皮？
<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 4 * 30</gadget>
<output>60</output>

<result>60</result>