QUESTION 4 A random sample of 85 group leaders, supervisors, and similar personnel at General Motors revealed that, on the average, they spent 6.5 years on the job before being promoted. The standard deviation of the sample was 1.7 years. You may use 3 decimal places in your calculations/answers. a) How many degrees of freedom are there? b) What t-value do we need to use for a 98% confidence interval? c) What is the standard error of the mean? d) Determine the 98% confidence interval for the average class grade. hs to