3. A culture of the bacterium Salmonella enteritidis initially contains 50 cells. When introduced into a nutrient broth, the culture grows at a rate proportional to its size. After 1.5 hours the population has increased to 975 . (a) Find an expression for the number of bacteria after 3 hours. (b) Find the number of bacteria after 3 hours. (0) Find the rate of growth after 3 hours. (d) After how many hours will the population reach 250,000