A random sample of 18 observations produced a sample mean of 9.24. Find the critical and observed values of z for each of the following tests of hypothesis using .05. The population standard deviation is known to be 5.40 and the population distribution is normal.
a. H0: µ = 8.5 versus H1: µ ≠ 8.5
b. H0: µ = 8.5 versus H1: µ > 8.5