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 who 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, owners were found that drove roughly the same mileage. The cost statistics are y_A = $87.00/1,000 miles, y_B = $75.00/1,000 miles, S_A = $5.99, and SB — $4.85. Compute a 95% confidence interval to estimate μ_A — μ_B, the difference in the mean operating costs. Assume normality and equal variance.