There is a cube with a side length of 9 cm. A square hole with a side length of 2 cm is drilled in the center of every two opposite sides and penetrates. What is the volume of the obtained solid?
有一个棱长为9厘米的正方体，在每两个对面的中央钻一个边长为2厘米的正方形孔，且穿透，所得立体的体积是多少？
<gadget id="calculator">9 * 9 * 9</gadget>
<output>729</output>

<gadget id="calculator">2 * 2 * 9 * 3</gadget>
<output>108</output>

<gadget id="calculator">729 - 108</gadget>
<output>621</output>

<gadget id="calculator">2 * 2 * 2 * 2</gadget>
<output>16</output>

<gadget id="calculator">621 + 16</gadget>
<output>637</output>

<result>637</result>