A tank with capacity of gal of water originally contains gal of water with lb of salt in solution. Water containing lb of salt per gallon is entering at a rate of gal/ min, and the mixture is allowed to flow out of the tank at a rate of gal/ min. Let lb. be the amount of salt in the tank, 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 (Q(t)). Find the concentration (in pounds per gallon) of salt in the tank when it is on the point of overflowing.