Margaret knows that the weekly average amount of time a student living in the dorms actually

Margaret knows that the weekly average amount of time a student living in the dorms actually spends in the dorm follows a normal curve with mean of 92 hours with variance of 81 nationwide.
a. what is the probability that a randomly chosen student has a weekly average amount of time in the dorms between 100 hours and 110 hours?

b. what is the proportion of students that have a weekly average amount of time in the dorms between 80 hours and 110 hours?