So, if Jon's car can travel #35# miles on one gallon of fuel, then dividing the total miles the car needs to travel by the number of miles that the car can travel per gallon of fuel will give us the number of gallons the car needs to travel #x# distance (in this case, #656# miles).

So

#656/35 = "18.7428571429 gallons"#

and assuming we are rounded to two decimal places, it would be #18.74# gallons.