Two independent random samples of size n1 = 24 and n2 = 20 are taken from the two normal populations. The sample means are x1-bar = 220 and x2-bar = 240. The variances are sigma1^2 = 15 and sigma2^2 = 18. Find the following:
a) a 90% two sided confidence interval on Mu2 - Mu1.
b) a 99% upper confidence interval on Mu2 - Mu 1.