I set the prices and liters in a ratio. For instance, when I set Esso's numbers up I did...
20.25/25 and cross multiplied with the denominator being one liter and the numerator being X. I ended up getting .81 which was the lowest price per liter. Petro Can. ended up being .89 cents and Shell was the most expensive being 1.25 dollars per liter. Esso is the cheapest therefore is the best deal. Hope this helps!!! Good luck with the assignment!!!