In Problem 13.4 on page 531, the marketing manager used shelf space for pet food to predict weekly sales. The data are stored in Petfood. For these data, SYX = 30.81 and ht = 0.1373 when X = 8.
a. Construct a 95% confidence interval estimate of the mean weekly sales for all stores that have 8 feet of shelf space for pet food.
b. Construct a 95% prediction interval of the weekly sales of an individual store that has 8 feet of shelf space for pet food.
c. Explain the difference in the results in (a) and (b).