A sample of 35 textbooks was taken from the TCU bookstore. The average price of the books was $52.50 with a standard deviation (S) of $5.10. Forty textbooks were sampled from the SMU bookstore. The average price of those 40 books was $65.00 with a variance (S2) of $18.06. Calculate a 90% confidence interval for the difference in the average prices for the two stores. Explain your findings.