A simple mixing process follows first-order behavior. A 200-gal mixing tank process, initially at steady state, is shown in Fig. P4–17. At time t = 0, the inlet flow is switched from 5% salt to freshwater. What does the inlet flow rate need to be to reduce the exit concentration to less than 0.5% in 30 min?

Salt Water e 5% salt Volume = 200 gal FIGURE P4-17