7. Refer to Exercise 5. The means of two of the factorlevel combinations—say, A B 1 1 and A B 2 1—are 8.3 1 x 5 and 6.3 2 x 5 , respectively. Find a 95% confidence interval for the difference in the mean response for factorlevel combinations A B 1 1 and A B 2 1.