The initial ultimate BOD after mixing of the Bergelmir Riveris 12.0 mg/L. The DO in the Bergelmir River after the wastewaterand river have mixed is at saturation. The river temperature is 10degrees celsius, the deoxygenation rate constant (kd) is 0.30 perday, and the reaction rate constant (kr) is 0.40 per day,Determine the critical point (tc) and the critical DO.