A cylindrical oil drum without a lid has a base diameter of 40 cm and a height of 50 cm. How much iron sheet is needed to make 10 such oil drums?
一种无盖的圆柱形油桶，底面直径是40厘米，高是50厘米．做10个这样的油桶至少需要多少铁皮？
<gadget id="calculator">3.14 * 40 * 50</gadget>
<output>6_280</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

<gadget id="calculator">6_280 + 1_256</gadget>
<output>7_536</output>

<gadget id="calculator">7_536 * 10</gadget>
<output>75_360</output>

<result>75_360</result>