Xuanxuan has a glass fish tank, 50cm long, 20cm wide, and 25cm high. Xuanxuan put a rockery into the fish tank, and the height of the water surface changed from 15cm to 18cm. What is the volume of this rockery?
宣宣家有一个玻璃鱼缸，长50cm，宽20cm，高25cm．宣宣将一座假山放入鱼缸中，水面高度由原来的15cm变成了18cm．这座假山的体积是多大？
<gadget id="calculator">18 - 15</gadget>
<output>3</output>

<gadget id="calculator">50 * 20 * 3</gadget>
<output>3_000</output>

<result>3_000</result>