3) (15 points) Each day, 10 million gallons (MGD) of wastewater containing a conservative pollutant at a concentration of 5.0 mg/L is released into a stream having an upstream flow

of 20 MGD and concentration of the same pollutant of 2.0 mg/L. Assuming the stream is instantaneously well-mixed,what is the concentration of the pollutant (in ppm) just downstream?