Here's the way I'd approach this problem. Well they tell you the ratio is 4:3 of green:white and you are given amounts of paint you have for green and white. You can kinda think of this as a limiting reagent problem. If you are given amounts of white and green paint, realize that unless they are in a ratio of 4:3 (which these amounts are not), one color is going to limit the amount of the other color. In this case, 1 gallon of white paint can be completely used up with 1 1/3 gallons of green paint (using the 4:3 ratio). From here, take 7/3 gallons (the total amount of paint used) and convert to quarts, then multiply by 120. That's the simplest way I can think of to approach it.
