Find the critical value z a/2 needed to construct a confidence interval with the given level....level 99.7%

The general social survey asked 1972 adults how many years of education they had. The sample mean was 13. 37 years with a standard deviation of 3.13 years. Construct a 98% confidence interval for the mean number of years of education.

a. constructs a 98% confidence interval for the mean number of years of education?

b. data collected in an earlier study suggests that the mean ten years ago was 13.28 years. A sociologist believes that the mean now is the same. Does the confidence interval contradict this believe? Explain