4) a. A group of doctors on a particular hospital identified that they attend an average of (15+ A) patients per hour. Assume the standard deviation is 4. A random sample of 36 hours was chosen. Find the 95% confidence interval. (14 Marks) b. Find the 90% confidence interval for the variance if a study of (9+ A) students found the 6.5 years as standard deviation of their ages. Assume the variable is normally distributed. (12 Marks)