A consumer group is interested in comparing operating costs for two different types of automobile engines. The group is able to find 15 owners whose cars have engine type A and 15 whose cars have engine type B. All 30 owners bought their cars at roughly the same time, and all have kept good records for a certain 12-month period. In addition, these owners drove roughly the same number of miles. The cost statistics are ¯yA = $87.00/1000 miles, ¯yB = $75.00/1000 miles, sA = $5.99, and sB = $4.85. Compute a 95% confidence interval to estimate μA − μB, the difference in the mean operating costs. Assume normality and equal variances.