A cylindrical oil barrel has a base radius of 4dm and a height of 5dm. How many square meters of iron sheet are needed to make such a pair of oil barrels?
一个圆柱形油桶，底面半径是4dm，高是5dm，做这样一对油桶需要多少平方米铁皮？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16 * 2</gadget>
<output>100.48</output>

<gadget id="calculator">2 * 3.14 * 4 * 5</gadget>
<output>125.6</output>

<gadget id="calculator">100.48 + 125.6</gadget>
<output>226.08</output>

<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">226.08 * (1/50)</gadget>
<output>4.5216</output>

<result>4.5216</result>