To compare two kinds of bumper guards, six of each kind were mounted 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):

Bumper guard 1: 127 168 143 165 122 139

Bumper guard 2: 154 135 132 171 153 149

Use the four steps to test at the 0.01 level of significance whether the difference between the means of these two samples is significant.