A cuboid fish tank is 40cm long, 20cm wide, and the original water height is 6cm. Place a craft stone so that it is completely soaked in water, and the water height becomes 7cm (the water does not overflow). Find the volume of the stone.
长方体鱼缸长40cm，宽20cm，原有水的高度6cm，放置一块工艺石，使其完全浸湿在水中，水的高度变为7cm(水未溢出)，求石头的体积．
<gadget id="calculator">7 - 6</gadget>
<output>1</output>

<gadget id="calculator">40 * 20 * 1</gadget>
<output>800</output>

<result>800</result>