Mingming’s fish tank is a cuboid with a length of 4 meters and a width of 3 meters. The height of the water level is 4.5 meters before the fake coral stones are placed, and 7.5 meters after the coral stones are placed. What is the volume of the fake coral stones?
明明家的鱼缸是一个长方体，长4米，宽3米，放上假珊瑚石前水位高度是4.5米，放上珊瑚石后是7.5米，假珊瑚石的体积是多少．
<gadget id="calculator">7.5 - 4.5</gadget>
<output>3</output>

<gadget id="calculator">4 * 3 * 3</gadget>
<output>36</output>

<result>36</result>