To make a cylindrical tin bucket without a cover, the diameter of the bottom surface is 8 decimeters, and the height is 2.5 decimeters. How many square decimeters of iron sheet should be used to make this bucket?
做一个无盖的圆柱体铁皮水桶，底面直径8分米，高2.5分米，做这个水桶至少要用铁皮多少平方分米？
<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<gadget id="calculator">31.4 + 50.24</gadget>
<output>81.64</output>

<result>81.64</result>