When performing a x2 test of independence in a contingency table with r rows and c columns, determine the upper-tail critical value of the test statistic in each of the following circumstances:
a. a = 0.05, r = 4 rows, c = 5 columns
b. a = 0.01, r = 4 rows, c = 5 columns
c. a = 0.01, r = 4 rows, c = 6 columns
d. a = 0.01, r = 3 rows, c = 6 columns
e. a = 0.01, r = 6 rows, c = 3 columns