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