The BOD<sub>5</sub> of an effluent from a coke oven plant is 25 mg/L, and the effluent discharge is 4 ML/d. The receiving stream has a BOD<sub>5</sub> of 2 mg/L and the stream flow is 40 ML/d. What will be the BOD<sub>5</sub> in the stream just below the mixing zone?

Correct Answer: 4.1