To make a cubic tin water tank without a cover, the side length is 9 decimeters, at least how many square decimeters of tin should be used?
做一个无盖的正方体铁皮水箱，棱长是9分米，至少用多少平方分米的铁皮？
<gadget id="calculator">9 * 9 * 5</gadget>
<output>405</output>

<result>405</result>