EPA miles per gallon ratings are obtained for all models of cars sold in the United States. One of these figures purports to represent mileage in combined city-country driving. Suppose a consumer group test drives 9 cars of a model with an EPA rating of 25.4 miles per gallon. Assume that population standard deviation (sigma) is equal to 2.1. Compute a 99% confidence interval (CI) for the true mean mileage. Please show all your work