A cuboid water tank measures 40cm in length, 30cm in width, and 35cm in depth from the inside. The depth of water inside is 10cm. When a cube iron block with a side length of 20cm is placed in it, what is the height of the water in centimeters?
一个长方体水箱，从里面量得长40cm，宽30cm，深35cm，里面的水深10cm，放进一个棱长20cm的正方体铁块后，水面高多少厘米．
<gadget id="calculator">40 * 30</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 * 10</gadget>
<output>12_000</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">1_200 - 400</gadget>
<output>800</output>

<gadget id="calculator">12_000 / 800</gadget>
<output>15</output>

<result>15</result>