A company sends a random sample of 16 of its salespeople to a course designed to increase their motivation and, hence, presumably their effectiveness. In the following year these people generated sales with an average value of $625,000 and a sample standard deviation of $80,000. During the same period, an independently chosen random sample of 10 salespeople who had not attended the course obtained sales with an average value of $608,000 and a sample standard deviation of $73,000. Assume that the two population distributions are normal and have the same variance. Find a 90% confidence interval estimate for the difference between the population mean sales for salespeople who attended the motivational course and for those salespeople who did not attend the course.