To make a tin chimney with a length of 2 meters and a width and height of 4 decimeters, at least how many square meters of tin chimney should be used?
要制作一节长2米，宽和高都是4分米的铁皮烟囱，至少要用多少平方米的铁皮？
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 2 * 4</gadget>
<output>16/5 = around 3.2</output>

<result>16/5 = around 3.2</result>