The class sizes of elementary school classes in a public school district are normally distributed with an unknown population mean and standard deviation. a random sample of 27 classes is taken and results in a sample mean of 20 students and sample standard deviation of 6 students. the margin of error for a 98% confidence interval estimate for the population mean using the student's t-distribution is 2.86. find a 98% confidence interval estimate for the population mean using the student's t-distribution.