A sample of 230 observations is selected from a normal population with a population standard deviation of 26. The sample mean is 18. a. Determine the standard error of the mean. (Round your answer to 3 decimal places.) Standard error of the mean c. Determine the 98% confidence interval for the population mean. (Use z Distribution Table.) (Round the z-value to 2 decimal places and final answers to 3 decimal places.) Confidence interval and c. The sample size is 8 and the level of confidence is 99%.