How many square decimeters of iron sheet should be used to make a cylindrical open bucket with a bottom diameter of 6 decimeters and a height of 8 decimeters? (Note that the answer must be expressed in a formula containing π, otherwise no points will be scored!)
用铁皮做一个底面直径为6分米，高为8分米的圆柱形无盖水桶，至少要用多少平方分米的铁皮．(注意答案要求用含π的式子表示，否则不计分！)
<result>57</result>