AP Calculus AB Problem

6. The rate at which raw sewage enters a treatment tank is given by E(t) = 850 + 715 cos (nt2/9) gallons per hour for O s t s 4 hours. Treated sewage is removed from the tank at a constant rate of 645 gallons per hour. The treatment tank is empty at time t = 0. (a) At what rate is the sewage entering the tank when t = 3 hours? (b) How many gallons of sewage enter the treatment tank during the time interval 0 s t s 4? Round your answer to the nearest gallon. (c) How many gallons of sewage are in the tank at t = 3 hours