A car can travel for a distance of 350 miles in = 20 gallons The car can travel for a distance of 1 mile in = (20/350) gallons = 2/35 gallons Then The same car can travel for a distance of 875 miles in = (2/35) * 875 gallons = 1750/35 gallons = 50 gallons So it can be seen that 50 gallons of gasoline is required to travel for a distance of 875 miles. I hope the procedure is clear enough for you to understand.
