Complete parts (a) through (c) below. (a) determine the critical value(s) for a right-tailed test of a population mean at the α=0.01 level of significance with 15 ˚ of freedom. (b) determine the critical value(s) for a left-tailed test of a population mean at the α=0.10 level of significance based on a sample size of n=20. (c) determine the critical value(s) for a two-tailed test of a population mean at the α=0.05 level of significance based on a sample size of n=14.