A cuboid water tank is 100cm long and 80cm wide when measured from the inside. When a piece of iron is completely submerged in the water, the water level rises 4cm. If the length of the iron block is 40 cm and the width is 20 cm, what is its height in cm?
一个长方体水槽，从里面量长100cm，宽80cm，把一块铁块完全浸入水中时，水面上升了4cm．如果铁块的长是40cm，宽是20cm，它的高是多少厘米？
<gadget id="calculator">40 * 20</gadget>
<output>800</output>

<gadget id="calculator">4 / 800</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">100 * 80 * (1/200)</gadget>
<output>40</output>

<result>40</result>