K.Brew sells a wide variety of outdoor equipment and clothing. The company sells both through mail order and via the internet. Random samples of sales receipts were studied for mail-order sales and internet sales, with the total purchase being recorded for each sale. A random sample of 11 sales receipts for mail-order sales results in a mean sale amount of $67.50 with a standard deviation of $23.75. A random sample of 7 sales receipts for internet sales results in a mean sale amount of $81.60 with a standard deviation of $23.25. Using this data, find the 90 % confidence interval for the true mean difference between the mean amount of mail-order purchases and the mean amount of internet purchases. Assume that the population variances are not equal and that the two populations are normally distributed. Construct the 90% confidence interval. Round your answers to two decimal places.