A random sample of 70 12th-grade students was asked how long it took to get to school. The sample mean was 15.9 minutes and the sample standard deviation was 12.2 minutes. a. Find a 95% confidence interval for the population mean time it takes 12th-grade students to get to school. b. Would a 90% confidence interval based on this sample data be wider or narrower than the 95% confidence interval? Explain. Check your answer by constructing a 90% confidence interval and comparing the width of the interval with the width of the 95% confidence interval you found in part (a).