A square-based rectangular aquarium is filled with water. The side length of the base is 40 cm. The height of the aquarium is 50 cm. The height of the water is equal to half the height of the aquarium. A solid cube with side length 20 cm is
then thrown into the aquarium and sinks to the bottom.

Does the water level now reach the top of the tank? If not, how far below the top
of the tank does the water reach?