please help and explain in detail how to do it.

I am not in a rush to get an answer so please explain in detail so I could understand. Thank you!

There are two elementary schools on Folly Beach. Third graders in both schools recently took the same standardized test. A random sample of 100 third graders from the first school has a mean exam score of 75. A random sample of 100 third graders from the second school has a mean score of 78. Assume the population standard deviation of the tests scores for the first school is 12 and 5 for the second school. Construct a 95% confidence interval for the true difference between the mean exam scores for the two schools. Round the endpoints of your interval to the nearest tenth.