How would I determine the critical? value(s) for a? right-tailed test of a population mean at the α = 0.01 level of significance with 20 degrees of freedom? Also, how would I determine the critical? value(s) for a? left-tailed test of a population mean at the α =0.05 level of significance based on a sample size of n = 15 and then determine the critical? value(s) for a ?two-tailed test of a population mean at the α =0.01 level of significance based on a sample size of n = 13?