A cylindrical iron chimney with a bottom diameter of 30 cm and a height of 2 meters. To make such a chimney with 20 knots, how many square meters of iron sheet should be used at least?
一节圆柱形状的铁皮烟囱，底面直径是30厘米，高是2米．做20节这样的烟囱，至少要用多少平方米铁皮？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3.14 * (3/10) * 2 * 20</gadget>
<output>37.68</output>

<result>37.68</result>