2.16. Refer to Plastic hardness Problem 1.22. a Obtain a 98 percent confidence interval for the mean hardness of molded items with an elapsed time of 30 hours. Interpret your confidence interval. b. Obtain a 98 percent prediction interval for the hardness of a newly molded test item with an elapsed time of 30 hours. c. Obtain a 98 percent prediction interval for the mean hardness of 10 newly molded test items, each with an elapsed time of 30 hours. d. Is the prediction interval in part (c) narrower than the one in part (b)? Should it be? e. Determine the boundary values of the 98 percent confidence band for the regression line when Xh = 30. Is your confidence band wider at this point than the confidence interval in part (a)? Should it be