A cylindrical oil barrel has a base radius of 10dm and a height of 20dm. How much iron sheet is needed to add a cover to this oil drum, and what is it actually asking for?
一个圆柱形油桶，底面半径是10dm，高是20dm．给这个油桶加个盖需要多大的铁皮，实际是求的什么？
<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>