Chapter 2.3, Problem 2P

A tank initially contains $200L$ of pure water. A mixture containing a concentration of $\gamma g/L$ of salt enters the tank at a rate of $4L/\min$, and the well-stirred mixture leaves the tank at the same rate. Find an expression in terms of $\gamma$ for the amount of salt in the tank at any time $t$. Also find the limiting amount of salt in the tank as $t\to \infty$.