Eddie Clauer sells a wide variety of outdoor equipment and clothing. The company sells both in-store and online. Random samples of sales receipts were studied for in-store sales and online sales, with the total purchase being recorded for each sale. A random sample of 11 sales receipts for in-store sales results in a mean sale amount of $81.20 with a standard deviation of $23.75. A random sample of 19 sales receipts for online sales results in a mean sale amount of $98.00 with a standard deviation of $25.25. Using this data, find the 90% confidence interval for the true mean difference between the mean amount of in-store purchases and the mean amount of online purchases. Assume that the population variances are not equal and that the two populations are normally distributed. Step 1 of 3: Find the critical value that should be used in constructing the confidence interval. Round your answer to three decimal places.