"To test the effect of alcohol in increasing reaction time to respond to a given stimulus, the reaction times of 100 people were measured. After consuming 3oz of alcohol, the reaction time for each of the 100 people were measured again. The mean difference in reaction time was -1.07 seconds (where the difference of BEFORE-AFTER was calculated with a standard deviation of 7.22. Find a 90% confidence interval for the mean difference in the reaction time."

I'm not sure how to find a confidence interval. How do I go about setting it up and solving this question?