There is a cuboid water tank with a length of 5 decimeters, a width of 4 decimeters, and a height of 3 decimeters. Originally, the water depth inside was 1 decimeter. After a stone was put in (the stone completely sank to the bottom of the water), the water depth became 2.5 decimeters. What is the volume of this stone?
有一个长方体的水缸，长5分米，宽4分米，高3分米，原来里面的水深1分米，放进一块石头后(石头完全沉入水底)，水深变为2.5分米，这块石头的体积是多少？
<gadget id="calculator">2.5 - 1</gadget>
<output>1.5</output>

<gadget id="calculator">5 * 4 * 1.5</gadget>
<output>30</output>

<result>30</result>