State the total degrees of freedom for the following t tests: (a) n = 12 for a one-sample t test (b) Critical value = 1.645 for a one-tailed test, a = .05 (c) df1 - 12, n2 = 19 for a two-independent-sample t test (d) Critical value = 63.657 for a two-tailed test, a = .01