To compare two kinds of front-end design, six of each kind were installed on a certain make of compact car. Then each car was run into a concrete wall at 5 miles per hour, and the following are the costs of the repairs (in dollars):
Design 1: 127, 168, 143, 165, 122, 139
Design 2: 154,135, 132, 171,153,149
Use four steps to test at 0.01 level of significance whether the difference between the means of these two samples is significant.