I think you would just have to find the square roots
Kelly traveled 50 miles with 20 gallons, 50/20 = 2.5 miles per gallon
Andy traveled 78.75 miles with 15 gallons, 78.75 / 15 = 5.25 miles per gallon
Rick traveled at 4.8 gallons per mile
Andy traveled furthest.
If you divide that HUGE number by 500 you get 2.95147905e17
Hope this helps!