1. Find how much gas can be obtained: $10 goes into $2.50 4 times, so you can get 4 gallons.
2. Find how much gas is in the car: 1/4 of the maximum 13 gallons is 3.25 gallons, so there is already 3.25 gallons in your car.
3. Find how many gallons you have total: 4 gallons + 3.25 gallons =
7.25 gallons