Answer:
Well, first. A trip of 100 miles in 1/6 less than the 600 mile trip. So, we also know that a 600 mile trip uses 60 gallons. In order to find the amount used in a 100 mile trip, just divide 60 gallons by 6!
60 / 6 = 10
Which means, that in a trip of 100 miles. 10 gallons of fuel are used!