The Local Swim Team Is Considering Offering a New Semi-Private $\sigma$

The local swim team is considering offering a new semi-private class aimed at entry-level swimmers, but needs at minimum number of swimmers to sign up in order to be cost effective.Last year's data showed that during 8 swim sessions the average number of entry-level swimmers attending was 15.Suppose the instructor wants to conduct a hypothesis test.The alternative hypothesis for this hypothesis test is: "the population mean is less than 15".The sample size is 8, $\sigma$ is known, and α =.05, the critical value of z is _______.

A) 1.645
B) -1.645
C) 1.96
D) -1.96
E) 2.05