If anyone could help with this problem it would help a lot

We are conducting a study of wages of assembly-line workers in a major manufacturing company located in the city of Old Pueblo. There are several hundred assembly-line workers in the firm. We need to get a good idea of the mean hourly wage of this population of employees. To do so, we randomly select 20 personnel files of assembly-line workers and we record the hourly wages of these employees. In this sample we find a mean wage of $21.00 and a standard deviation of $5.00. a) Which statistic should we use in order to construct a confidence interval: Z or t? Why? b) Compute a 95 percent confidence interval for the mean hourly wage of the company's assembly-line workers. c) Suppose we wanted to be more confident. Compute the 98% confidence interval for the mean