6. A random sample of n= 12 observations was drawn and ordered as follows. 81, 94, 95, 95, 97, 102, 106, 110, 113, 114, 135, 160 (a) Find the mean of the sample. (1 mark) (b) Find the standard deviation of the sample (Sn-1). (3 marks) (c) The sampling distribution of the sample mean follows a t-distribution. What is the degree of freedom of the t-distribution? (1 mark) (d) Find the 99% confidence interval for the population mean. (2 marks)