In a rectangular parallelepiped glass tank with a length of 50 cm and a width of 40 cm, there is a square iron block with a side length of 20 cm. The iron block is completely submerged. At this time, the water depth is 40 cm. If the iron block is taken out, how deep is the water in the tank?
在一个长50厘米，宽40厘米的长方体玻璃缸中，有一块棱长为20厘米的正方体铁块，铁块完全浸没，这时水深40厘米，若把铁块取出，缸中水深多少厘米？
<result>16</result>