(3) To compare two kinds of bumper guards, 6 of each kind were mounted on a certain make of 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 (a) Test at the 0.01 level of significance whether the mean repair costs are different between the cars using these two bumper guards. What assumptions did you make? (b) Also find a 99% confidence interval for the difference in the mean repair costs between the cars using the two bumper guards. What assumptions did you make? Based on the confidence interval, can you say that the two bumper guards result in different repair costs?