You work for a rental car company. If customers return a car with under half a tank of gas, they are charged $8 per gallon of gas to fill up the tank. Otherwise, it costs $4 per gallon of gas to fill up the tank. A customer returns a rental car that has a tank capacity of 16 gallons. If the rental car is returned with 800 fluid ounces of gasoline in it, how much should you charge the customer to fill the tank?