please answer 6 and 7 only if you know

6. A company spilled a contaminant that got into the water distribution system of a small town, which has an average flow of 100,000 gpd. The contaminant infiltrated a pipe 1,500 ft from the storage tank, and the concentration at the infiltration point is 5 mg/L. The storage tank has a volume of 125,000 gallons and the first user is 500 ft from the storage tank. Assume velocity of 2.5 ft/s in pipes, and a rate constant of 3/day. What is the concentration at the first user? (15) 7. A PFR is not meeting effluent requirements so baffles are going to be added to the tank to increase contact time. The tank is 12 ft deep, 40 ft wide, and 120 ft long. The engineer is going to add long baffles to the tank. The baffles will be 90% of the tank length. If the current HRT is 0.5 d, and the influent concentration is 9 mg/L with an effluent limit of 1.5 mg/L, how many baffles need to be added? Assume k-1.98/day