(10 points) 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. a random sample of 36 stores this year shows mean sales of 75 units of a small appliance with a standard deviation of 6 units. during the same point in time last year, a random sample of 49 stores had mean sales of 68 units with standard deviation 7 units. it is of interest to construct a 95 percent confidence interval for the difference in population means −, where is the mean of this year's sales and is the mean of last year's sales. enter values below rounded to three decimal places. (a) the estimate is: . (b) the standard error is: .