Location is known to affect the number, of a particular item, sold by an automobile dealer. two different locations, a and b, are selected on an experimental basis. location a was observed for 9 days and location b was observed for 13 days. the number of the particular items sold per day was recorded for each location. on average, location a sold 39 of these items with a sample standard deviation of 9 and location b sold 51 of these items with a sample standard deviation of 6. select a 95% confidence interval for the difference in the true means of items sold at location a and b.