I want to figure out the C0 and C infinite for both case.

A lake bas reached steady state conditions with a pollutant concentration of 5 mg/L, a sewage treatment plant nearby suddenly starts to continuously discharge 30mg/L of the same pollutant to this lake. After a long time, a new steady-state condition was reached in the lake with a new steady-state concentration at 10 mg/L. You can setup the transient-state mass balance with C0 value of mg/L and Cm value of mg/L to find out the sewage concentration in the lake, 2 weeks after the introduction of the sewage. If the sewage discharge is then eliminated after the steady-state conditions were reached, yhu can again setup the transient-state mass balance with C0 value of mg/L and Cmvalueof sewage concentration in the lake 2 weeks after the elimination of the sewage discharge