a random sample of 10 waitresses in iowa city, iowa, revealed the following hourly earnings, included tips: 19, 18, 15, 16, 18, 17, 16, 18, 20, and 14. (units are dollars) if the hourly earnings are normally distributed with a population standard deviation of $4.50. you want to calculate a 95% confidence interval for the mean hourly earnings for all waitresses in iowa city. what is the value of the point estimate