Sharon worked hard for a long time to save the money for a new car. She has budgeted between $15,000 and $20,000 for the new car plus the cost of gas for a year. Let x represent gas mileage. Which compound inequality represents the gas mileage that a $12,000 car can get and still fit in her budget if gas costs $4 per gallon and she drives 15,000 miles a year?