This exercise uses the population growth model. A certain culture of the bacterium Rhodobacter sphaeror'des initially has 15 bacteria and is observed to double every 6 hours. (a) Find an exponential model n[t) = n02\"? for the number of bacteria in the culture after t hours. ME) = [b] Estinate the number of bacteria after 17 hours. (Round your answer to the nearest whole number.) (c) After how many hours will the bacteria count reach 1 million? [Round your answer to one decimal place.)