A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were involved in accidents over a 1-year period. Those with the special bumper are the test group and the other vehicles are the control group, shown below. Each "repair incident" is defined as an invoice (which might include more than one separate type of damage). Statistic Test Group Control Group Mean Damage X1 = $ 1,245 X2 = $ 1,790 Sample Std. Dev. S1 = $ 721 S2 = $ 835Repair Incidents n1 = 17 n2 = 14 Source: Unpublished study by Thomas W. Lauer and Floyd G. Willoughby. A) Construct a 99 percent confidence interval for the true difference of the means assuming equal variances. B) Repeat part (a), using the assumption of unequal variances with Welch's formula for d. f.C) Did the assumption about variances change the conclusion? D) Construct separate 99% confidence intervals for each mean.