Suppose the heights of 18-year-old men are approximately normally distributed, with mean 67 inches and standard deviation 5 inches. (a) what is the probability that an 18-year-old man selected at random is between 66 and 68 inches tall? (round your answer to four decimal places.) (b) if a random sample of twelve 18-year-old men is selected, what is the probability that the mean height x is between 66 and 68 inches? (round your answer to four decimal places.)