What metric is used to express the change in gas price per gallon in Dave's case?

The change in gas price per gallon is expressed in terms of dollars per gallon. This metric allows consumers to understand how much they are paying for each gallon of gas, making it easier to compare prices at different gas stations or over time. It reflects the cost that consumers need to anticipate when budgeting for fuel expenses.

By using dollars per gallon as a unit, one can directly assess the impact of price fluctuations on their overall fuel costs, facilitating informed decisions regarding refueling and travel plans. The other options provided do not directly relate to the pricing metric; they involve quantities that either enhance the understanding of fuel consumption or relate to the vehicle itself, rather than conveying the cost of fuel specifically.