For the following stirred tank reaction, carry out the following analysis. a. Write an initial value problem for the mass of the substance. b. Solve the initial value problem. A 400-L tank is initially filled with pure water. A copper sulfate solution with a concentration of 20 g/L flows into the tank at a rate of 2 L/min. The thoroughly mixed solution is drained from the tank at a rate of 2 L/min.