11-24. The ABC corporation claims that its new gasoline additive for passenger cars will enhance the mileage per tankfull of gasoline if a can of their product is added to a full tank of gasoline. Five vehicles were tested, yielding the following results (miles per tankfull):

Vehicle 1 2 3 4 5 Before additive 370 385 375 380 378 After additive 387 397 380 392 389 Find a 95% confidence interval for the difference in the means of these two data sets.