Determine the critical values for the following tests of the population mean with an unknown population standard deviation. The analysis is based on 18 observations drawn from a normally distributed population at a 1% level of significance.
a. H0: µ ≤ 52 versus HA: µ > 52
b. H0: µ = 9.2 versus HA: µ ≠ 9.2
c. H0: µ ≥ 5.6 versus HA: µ > 5.6
d. H0: µ = 10 versus HA: µ ≠ 10