To make a pair of metal buckets without lids, the bottom radius of the bucket is 3 decimeters, and the height is 0.5 meters, how many square decimeters of metal buckets are needed at least.
制作一对无盖的铁皮水桶，水桶的底面半径为3分米，高为0.5米，至少需要多少平方分米铁皮．
<gadget id="calculator">2 * 3.14 * 3 * 0.5 * 10</gadget>
<output>94.2</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<gadget id="calculator">94.2 + 28.26</gadget>
<output>122.46</output>

<gadget id="calculator">122.46 * 2</gadget>
<output>244.92</output>

<result>244.92</result>