A Radio Station Claims That the Amount of Advertising Each $z = - 4.00$

Short Answer

A radio station claims that the amount of advertising each hour has a mean of 15 minutes and a standard deviation of 1.5 minutes. You listen to the radio station for 1 hour and observe that the amount of advertising time is 9 minutes. Calculate the z-score for this amount of advertising time.
A) $z = - 4.00$
B) $z = - 9$
C) $z = 0.50$
D) $z = 4.00$