For a 4-unit class like Statistics, students should spend average of 12 hours studying for the class. A survey was done on 30 students, and the distribution of total study hours per week is bell-shaped with a mean of 13 hours and a standard deviation of 2.5 hours. Use the Empirical Rule to answer the following questions. a) 68% of the students spend between hours and hours on Statistics each week. b) 95% of the students spend between hours and hours on Statistics each week. c) 99.7% of the students spend between hours and hours on Statistics each week.