4. (10 pts) In a large sample of customer accounts, a utility company determined that the average number of days that a bill was paid after being sent out was 32 with a standard deviation of 7 days. For all parts, show work or briefly explain how you got your answer. a) Assume the data to be approximately bell-shaped. Approximately what percentage of bills were paid between 25 days and 39 days after being sent out? b) Assume the data to be approximately bell-shaped. Approximately what percentage of bills were paid between 25 days and 46 days after being sent out? c) If we do not assume that the population is bell-shaped, at least what percentage of the bills were paid between 18 and 46 days after being sent out?