A simple random sample of size n is drawn from a population that is known to be normally distributed. The sample variance, s , is determined to be 12.1. Complete parts (a) through (c). (a) Construct a 90% confidence interval for of if the sample size, n, is 20. The lower bound is 7.63 . (Round to two decimal places as needed.) The upper bound is 22.72 . (Round to two decimal places as needed.) (b) Construct a 90% confidence interval for of if the sample size, n, is 30. The lower bound is (Round to two decimal places as needed.)