The initial ultimate BOD after mixing of the James River is 30 mg/L. The DO in the river after the wastewater and river have mixed is at saturation. The river temperature is 10°C. At 10°C, the deoxygenation rate constant, k, is 0.32 d¹ and the reaeration rate constant, k2 is 0.32 d¹. Determine the critical point te and the critical DO.