A river above a town has a flow of 200L/s and a BOD of 1mg/L. The river is receiving 25L/s of treated sewage ( BOD=25mg/L ) from the town and 25L/s of untreated effluent (BOD = 175mg/L ) from a pulp and paper mill just downstream from the town. If the BOD of the river just below the mill outfall must not exceed 5mg/L, show that the percent removal of organic matter (BOD) is required by the mill to meet this requirement is 90%. (Note: This is a basic mass balance problem, NOT a Streeter Phelps problem.)