Refer to the data file P08_66.xlsx. Comfy Company sells medium priced patio furniture through a mail-order catalog. It has operated primarily in the East but is now expanding to the Southwest. To get off to a good start, it plans to send potential customers a catalog with a discount coupon. However, Comfy is not sure how large a discount is needed to entice customers to buy. It experiments by sending catalogs to selected residents in six cities. Tucson and San Diego receive coupons for 5% off any furniture within the next two months, Phoenix and Santa Fe receive coupons for 10% off, and Riverside and Albuquerque receive coupons for 15% off.

Comfy wonders whether there are differences across pairs of cities that receive the same discount.

a. Calculate a 95% confidence interval for the difference between the mean amount spent for the following pairs of cities: (These means should include the "0 purchases." Round your answers to one decimal place, if necessary. If your answer is negative number, enter "minus" sign.)