3. A 1000 m³ well-mixed tank is filled with 100 mg/L of a conservative pollutant. Clean water is added to the tank at a flow rate of 100 m/d. What is the concentration of the pollutant (in mg/L) in the tank after 7 days? a) About 20 b)About 30 c) About 50 d) About 60 e) About 70

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