Confidence interval for the population mean

The weekty time (in hours) spent doing homework for 18 randomly selected high school students is listed below. 12.0 11.3 13.5 11.7 12.0 13.0 15.5 10.8 12.5 12.3 14.0 9.5 8.8 10.0 12.8 15.0 11.8 13.0 a. Construct a 99% confidence interval for the population mean. (Assume the times ore normally distributed). Interpret you results. (Round to the nearest 1000") b. Find the sample mean and the sample standard deviation. c. Repeat port a. now knowing that a = 1.8 minutes.