Problem 6: For another subject (a 29-year-old male) in the study by Diskin et al. (A-11), acetone levels were normally distributed with a mean of 870 and a standard deviation of 211 ppb. Find the probability that on a given day the subject's acetone level is: a) Between 600 and 1000 ppb b) Over 900 ppb c) Under 500 ppb d) Between 900 and 1100 ppb