To make a cubic iron sheet water tank without a cover, the bottom area is 0.81dm**2, how many square centimeters of iron sheet should be used at least?
做一个无盖的正方体铁皮水箱，底面积是0.81dm**2，至少用多少平方厘米的铁皮？
<gadget id="calculator">0.81 * 5</gadget>
<output>4.05</output>

<gadget id="calculator">4.05 * 100</gadget>
<output>405</output>

<result>405</result>