A cube goldfish tank with a side length of 4dm is filled with some water. The measured height from the bottom to the water surface is 2.5dm. Put an artificial coral stone piece. This means that the water surface rises to 3dm. Find the volume of this coral stone.
有一棱长是4dm的正方体金鱼缸里装了一些水，测得底部至水面高度为2.5dm，放入一个人造珊瑚石片，这是水面上升到3dm，求这个珊瑚石的体积．
<gadget id="calculator">3 - 2.5</gadget>
<output>0.5</output>

<gadget id="calculator">4 * 4 * 0.5</gadget>
<output>8</output>

<result>8</result>