Is there a significant difference in the gasoline mileage of a car for regular unleaded and premium unleaded? To test this question, a researcher randomly selected 15 drivers for a study. They were to drive their cars for one month on regular unleaded and for one month on premium unleaded gasoline. The participants drove their own cars for this experiment. The average sample difference was 2.85 miles per gallon in favor of the premium unleaded, and the sample standard deviation of difference was 1.9 miles per gallon. For α = .01, does the test show enough evidence for the researcher to conclude that there is a significant difference in mileage between regular unleaded and premium unleaded gasoline? Assume the differences in gasoline mileage figures are normally distributed in the population.