11. A manufacturing process that generates waste has to be shut down. This means starting at t=0, the concentration Cin entering a completely mixed flow reactor (CMFR) is set to 0. Assume a reaction that destroys the pollutant according to first-order kinetics, with k = 0.216/day. The reactor volume is 500 m, the volumetric flow rate of the single inlet and exit is 50 m/day. How long does it take the tank concentration to reach 10% of its initial, steady-state value? Hint: This is a non-steady-state problem. (10 pts)