A brine solution of salt flows at a constant rate of 8 L/min into a large tank that initially held 100 L of brine solution in which was dissolved 5 kg of salt. The solution inside the tank is kept well stirred and flows out at the same rate. If the concentration of salt in the brine entering the tank is 0.5 kg/L, determine the mass of the salt in the tank after minutes. When will the concentration of the salt in the tank reach 0.2 kg/L?