A research study on the sleeping habits of adults reported that X, the amount of sleep per night of U.S. adults follows a normal distribution with mean=7.5 hours and standard deviation=1.2 hours.

Using the Standard Deviation Rule, 2.5% of U.S. adults sleep more than how many hours per night?

(A)9.9

(B) 8.7

(C) 7.5

(D) 6.3

(E) 5.1