Well first you have to divide 620/20 which is 31. So his car goes 31 miles per gallon so you have 2 gallons and .25 of a gallon. So first off 2*31=62 miles then the 1/4 or .25. Multiply the 31 by .25 which is 7.75 now add 62 and 7.75 and you get how far his car can go.
