To make a pair of cylindrical tin buckets without a cover, the height is 40cm, and the diameter of the bottom surface is 30cm. How many square centimeters of iron are needed at least?
做一对无盖的圆柱形铁皮水桶，高是40cm，底面直径是30cm，至少需要铁皮多少平方厘米？
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">3.14 * 225</gadget>
<output>706.5</output>

<gadget id="calculator">3.14 * 30 * 40</gadget>
<output>3_768</output>

<gadget id="calculator">706.5 + 3_768</gadget>
<output>4_474.5</output>

<gadget id="calculator">4_474.5 * 2</gadget>
<output>8_949</output>

<result>8_949</result>