the answer would need 8 gallons.
it will normally not come to some one but i believe that you can not just get 1/2 of a gallon you can use 1/2 of a gallon so you need to round up even if the number should round down i needs to be rounded up since you can't have to less to travel a certain distance but you can have to much. so it is 8 gallons of gas
hope it helped