Find a confidence interval for u assuming that each sample is from a normal population. (Round the value of t to 3 decimal places and your final answers to 2 decimal places.) (a) x = 28, s= 4, n=7, 90 percent confidence. The 90% confidence interval is to (b) x = 43, s= 4, n = 19, 99 percent confidence. The 99% confidence interval is (c) x = 130, s = 15, n = 23, 95 percent confidence. The 95% confidence interval is to