A brine solution of salt flows at a constant rate of 4 L/min into a large tank that initially held 100 L of pure water. The solution inside the tank is kept well stirred and flows out of the tank at a rate of 3 L/min. If the concentration of salt in the brine entering the tank is 0.4 kg/L, determine the mass of salt in the tank after t min. When will the concentration of salt in the tank reach 0.2 kg/L? dx If x equals the mass of salt in the tank after t minutes, first express dt = input rate - output rate in terms of the given data. dx dt