A brine solution of salt flows at a constant rate of ​l/min into a large tank that initially held l of pure water. The solution inside the tank is kept well stirred and flows out of the tank at a rate of ​l/min. If the concentration of salt in the brine entering the tank is ​kg/l, determine the mass of salt in the tank after t min. When will the concentration of salt in the tank reach ​kg/l?.