help please lol

Sandra is comparing gasoline prices at two different gas stations. At Exxon gas station, the equation c=2.80g represents the equation between the number of gasoline g and c, the total cost for the gas. At the second gas station Sunoco, the cost of 2.5 gallons of gasoline is $8.30, and the cost of 5 gallons of gasoline is $16.60. How much money, per gallon, would Sandra save by going to the less expensive gas station?