The times per week a student uses a lab computer are normally? distributed, with a mean of 6.4 hours and a standard deviation of 1.1 hours. A student is randomly selected.Find the following probabilities.

?(a) Find the probability that the student uses a lab computer less than 4 hours per week. ?

(b) Find the probability that the student uses a lab computer between 6 and 8 hours per week. ?

(c) Find the probability that the student uses a lab computer more than 9 hours per week.