Confidence Interval Question

Hi,

I was hoping that someone could help me with the following question by showing me how to do it using confidence intervals. Although I've done it using the standard error, I want to know how to do it using confidence intervals, but I'm not sure how, as we are not given the sample mean (x bar).

*Experience with workers in a certain industry indicates that the time required for a randomlyselected worker to complete a job is approximately normally distributed with a standarddeviation of 12 minutes. If the sample mean is calculated as an estimate of the mean of allworkers, what is the relative accuracy of a measure based on a sample of 64 workers comparedwith one based on a sample of 16 workers?*

Thank you very much!

:)