Can students save money by buying their textbooks at Amazon

Can students save money by buying their textbooks at Amazon.com? To investigate this possibility, a random sample of 15 textbooks used during a recent semester at Miami University was selected. The prices for these textbooks at both a local bookstore and through Amazon.com were recorded. The prices for the textbooks, including all relevant taxes and shipping are given below.

(a) At the 0.01 level of significance, is there evidence of a difference between the mean price of textbooks at the local bookstore and Amazon.com?
(b) What assumption is necessary to perform this test?
(c) Construct a 99% confidence interval estimate of the mean difference in price. Interpret the interval.
(d) Compare the results of (a) and (c).