To make a cylindrical chimney with a length of 9 meters and a base radius of 5 decimeters, at least how many square meters of iron sheet is required.
做一个长9米，底面半径为5分米的圆柱形烟囱，至少需要多少平方米的铁皮．
<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 * 3.14 * (1/2) * 9</gadget>
<output>28.26</output>

<result>28.26</result>