Lake City has two shops, Zekes and Elmers, that handle the majority of the towns auto body

Question:

Lake City has two shops, Zeke€™s and Elmer€™s, that handle the majority of the town€™s auto body repairs. Seven cars that were damaged in collisions were taken to both shops for written estimates of the repair costs. These estimates (in dollars) are shown in the following table.

a. Construct a 99% confidence interval for the mean µd of the population paired differences, where a paired difference is equal to Zeke€™s estimate minus Elmer€™s estimate.
b. Test at a 5% significance level whether the mean µd of the population paired differences is different from zero.
Assume that the population of paired differences is (approximately) normally distributed.