Make a cube-shaped cardboard box without a lid, with a side length of 9 cm. At least how many square centimeters of cardboard should be used.
做一个不带盖的立方体形状的硬纸盒，棱长为9厘米．至少要用多少平方厘米硬纸板．
<gadget id="calculator">9 * 9 * 5</gadget>
<output>405</output>

<result>405</result>