Radio station hypothesis tests

WNAE, an all-news AM station, finds that the distribution of the lengths of time listeners are tuned to the station follows the normal distribution. The meanof the distribution is 15.0 minutes and the standard deviationis 3.5 minutes. What is the probabilitythat a particular listener will tune in:

a. More than 20 minutes?
b. For 20 minutes or less?
c. Between 10 and 12 minutes?

The solution explains how excel can be applied to a hypothesis question on radio stations.