8.12 The standard deviation for a population is o = 14.8. A random sample of 25 observations selected from this population gave a mean equal to 143.72. The population is known to have a normal distribution. a. Make a 99% confidence interval for H. b. Construct a 95% confidence interval for u. c. Determine a 90% confidence interval for . d. Does the width of the confidence intervals constructed in parts a through c decrease as the confidence level decreases? Explain your answer. T