A researcher wanted to determine if using an octane booster would increase gasoline mileage. A random sample of seven cars was selected; the cars were driven for two weeks without the booster and two weeks with the booster.

Miles / Gal Without	Miles / Gal With
26.91	29.86
20.03	27.47
26.27	28.14
29.1	26.17
22.71	27.08
29.5	27.28
27.83	25.89

Determine the difference betweenthe sample mean mileageof the cars thataredriven without a booster and with a booster.