5. (10 points) A pipe from a municipal wastewater treatment plant discharges 1.2 m3/s of poorly treated effluent containing 7.0 mg/L of phosphorus compounds (reported as mg P/L) into a river with an upstream flow rate of 20 m3/s and a background phosphorus concentration of 0.1 mg P/L. What is the resulting concentration of phosphorus (in mg P/L) in the river just downstream of the plant outflow (mg P/L)