6. In a study of the effect of cigarette smoking on the carbon monoxide diffusing capacity (DL) of the lung, researchers found that current smokers had DL readings significantly lower than those of either exsmokers or nonsmokers. The carbon monoxide diffusing capacities for a random sample of n = 20 current smokers are listed here: 103.762 88.602 73.003 123.086 91.052 92.295 61.675 90.677 84.023 76.014 100.615 88.017 71.210 82.115 89.222 102.754 108.759 73.154 106.755 90.479 a. Do these data indicate that the mean DL reading for current smokers is significantly lower than 100 DL, the average for nonsmokers? Use a = .01. b. Find a 99% upper one-sided confidence bound for the mean DL reading for current smokers. Does this bound confirm your conclusions in part a?