A 200-gallon tank is half full of distilled water . At time t=0, a solution containing 0.5 pound of concentrate per gallon enters the tank at the rate of 5 gallons per minutes, and the well-stirred mixture is withdrawn at the rate of 3 gallon per minutes.

At the time the tank is full (t=50mins), how many pounds of concentrate will it contain?

The ans is 82.32lb. can anyone tell me how to do it?