Vannex Inc. has received two large shipments of bluray amplifiers, one from supplier A and one from supplier B. You have tested a sample of 14 amplifiers from each shipment to determine if there is a difference in the average maximum volume without distortion between the units in the two shipments. The average maximum volume for the sampled units in shipment A is 260 decibels, with a standard deviation of 18 decibels; for the sample of units from shipment B, the sample average is 228 decibels, with a standard deviation of 21 decibels. Show the 90% confidence interval estimate for the difference in average maximum volume without distortion for the two shipments. (Assume the two population distributions are normal, with equal standard deviations.)