How many square centimeters of iron sheet should be used to make a cylindrical iron sheet ventilation pipe with a base radius of 15 cm and a length of 40 cm?
制作一个底面半径为15厘米、长为40厘米的圆柱形铁皮通风管，至少要用多少平方厘米铁皮？
<gadget id="calculator">2 * 3.14 * 15 * 40</gadget>
<output>3_768</output>

<result>3_768</result>