How to find the confidence interval

#1
Randomly selected 25 student cars have ages with a mean of 7.4 years and a standard deviation of 3.4 years, while randomly selected 15 faculty cars have ages with a mean of 5.2 years and a standard deviation of 3.3 years.
Construct a 99% confidence interval estimate of the difference μs−μf, where μs is the mean age of student cars and μf is the mean age of faculty cars.