To make a cubic tin water tank without a cover, the bottom area is 81dm**2, how many square decimeters of tin should be used at least?
做一个无盖的正方体铁皮水箱，底面积是81dm**2，至少用多少平方分米的铁皮？
<gadget id="calculator">81 * 5</gadget>
<output>405</output>

<result>405</result>