Alexandra uses her car for business. She knows that her tank was full when she started her business trip, but she forgot to write down the odometer reading at the beginning of the trip. When the trip was over the odometer read 13,020.5. Alexandra's car gets 25 miles per gallon. When she filled up the tank with gas that cost $2.45 per gallon, her total bill for the trip was $35.28. Determine Alexandra's beginning odometer reading.