A square liquid storage tank has plan-view dimensions (looking down from above) of 10m x 10m. Over a one day period, 300m^3 of liquid enters the tank, and the level of the tank rises 2 meters. How much liquid has left the tank?

How do I set this up?

A 2 meter rise means 200 m^3 has been added to stored liquid. If 300 m^3 was added, then 100 m^3 left the tank somehow.