Problem 4. A water treatment plant has six settling tanks that operate in parallel (the flow gets split into six equal flow streams), and each tank has a volume of 40 m. a) If the flow to the plant is 10 million gallons per day, what is the residence time in each of the settling tanks? b) If instead, the tanks operated in series (the entire flow goes first through one tank, then the second, and so on), what would be the retention time in each tank? c) The suspended solids concentration is 100 mg/L at the inlet of the plant. Assuming a first-order removal rate for suspended solids in the settling tanks with a rate constant k=0.1 min-!. What would be the suspended solids concentration at the outlet of the plant when the settling tanks are operated in parallel? 1 d) What would be the suspended solids concentration at the outlet of the plant when the settling tanks are operated in series instead