The amount of fuel remaining in a car's tank, $F$, in gallons, is a linear function of the distance driven, $D$, in miles. After driving 50 miles, there were 18 gallons of fuel remaining. After driving 200 miles, there were 12 gallons of fuel remaining. Based on this model, how many gallons of fuel were in the tank when the car started the trip (at 0 miles driven)?

Round your answer to the nearest tenth if necessary.