(1 point) A market research firm supplies manufacturers with estimates of the retail sales of their products from samples of retail stores. Marketing managers are prone to look at the estimate and ignore sampling error. An SRS of 22 stores this year shows mean sales of 82 units of a small appliance, with a standard deviation of 6.8 units. During the same point in time last year, an SRS of 31 stores had mean sales of 88.324 units, with standard deviation 6.6 units. A decrease from 88.324 to 82 is a drop of about 8%. 1. Construct a 99% confidence interval estimate of the difference /1 - /2, where ] is the mean of this year's sales and /2 is the mean of last year's sales. (a)