Testing equality of two means.

An independent testing agency has been contracted to determine whether there is any difference in gasoline mileage output of two different gasolines used in the same model automobile. The first gasoline was tested on 200 cars and produced a sample average of 18.5 miles per gallon with a standard deviation of 4.6 miles per gallon. The second was tested on a sample of 100 cars and produced a sample average of 19.34 miles per gallon with a standard deviation of 5.2 miles per gallon. At the .05 level of significance, is there evidence of a difference in performance of the two gasolines?