The Grinch is planning a marketing campaign for his new line of orange marbles. The most recent census only has population data for red, blue and green marble ownership, so he hires Cindy Lou Who to estimate the mean number of orange marbles per household in Whoville. CLW surveys a simple random sample of 750 Who-households and finds that the sample mean number of orange marbles per household is 15.3 with a (sample) standard deviation of 6.2. (a) (2 pts) Assuming that the distribution of orange marbles per household in Whoville is normal, and assuming that CLWs sample is fairly representative, approximately what percentage of Whoville households own between 13 and 17 orange marbles. (b) (4 pts) Use CLW's data to construct a 95%-confidence interval for the average number of orange marbles per household in Whoville