There is not enough information to answer this problem the way it is currently worded.
ASSUMING that if the total amount of money spent remains constant (a big assumption), then we need to find out how much was spent on 2,700 gallons of gas. That would be S = pg, where S is the total Sales in dollars, p is the price per gallon, g is the number of gallons sold. Substituting our known amounts, S = ($4.30)(2,700) = $11,610. Since gas is now selling at $4.10, and we have $11,610 we will spend on gas then, ($11,610) = ($4.10)g. Dividing both sides by $4.10 we get 2,831.707..... or since we are rounding to the nearest integer, ≈2,832 gallons.
An alternative way of solving this problem with the same assumptions, is noting that the S in both equations is the same S, so ($4.10)g = ($4.30)(2,700). Dividing both sides by $4.10 will yield the same answer as above with a little less computation.