In the Past, the Average Waiting Time Per Customer at a Fast

In the past, the average waiting time per customer at a fast food restaurant has been 7.5 minutes. The customer waiting time has a normal distribution. The manager claims that the use of a new cashier system will decrease the average customer waiting time in the store. A random sample of 16 customer transactions produces a mean waiting time of 6.3 minutes and a standard deviation of 2 minutes.
-At the 5% level of significance,how would we define the rejection region?

A) z < -1.645
B) z > 1.645
C) t > 1.753
D) t < -1.753
E) t < -1.782