rockery is placed in a cuboid fish tank with a bottom area of 54 square decimeters, and the water level rises by 4 cm. How big is the rockery?
在一个底面积为54平方分米的长方体鱼缸里放了一个假山石，水面上升了4厘米，这个假山石的体积有多大？
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">54 * (2/5)</gadget>
<output>108/5 = around 21.6</output>

<result>108/5 = around 21.6</result>