The standard deviation for a population is o = 15.7. A sample of 23 observations selected from this population gave a mean equal to 142.05. The population is known to have a normal distribution. Round your answers to two decimal places. a. Make a 99% confidence interval for u. b. Construct a 97% confidence interval for u. c. Determine a 95% confidence interval for u. i d. Does the width of the confidence intervals constructed in parts a through c decrease as the confidence level decreases