This is Differential Equations problem.Provide clean and clear solutions thank you.

4. A tank initially holds 410 liters of brine solution containing 7 kg of salt. At t=0, another brine solution containing 0.4 kg of salt per liter is poured into the tank at the rate of 18 liters/min. while the well-stirred mixture leaves the tank at the same rate. Find the (a) the amount of salt in the tank at any time t and (b) the time at which the mixture in the tank contains 15 kg of salt