Determine the number of degrees of freedom for the two-sample t test or CI in each of the following situations:
a. m = 10, n = 10, s1 = 5.0, s2 = 6.0
b. m = 10, n = 15, s1 = 5.0, s2 = 6.0
c. m = 10, n = 15, s1 = 2.0, s2 = 6.0
d. m = 12, n = 24, s1 = 5.0, s2 = 6.0