A tank with capacity of 900 gal of water originally contains 500 gal of water with 100 lb of salt in solution. Water containing 1 lb of salt per gallon is entering at a rate of 3 gal/ min, and the mixture is allowed to flow out of the tank at a rate of 2 gal/ min. Let Q(t) lb. be the amount of salt in the tank, V(t) gal be the volume of water in the tank.
Find the amount of salt in the tank at any time prior to the instant when the solution begins to overflow.