There are 4 quarts in a gallon and a quart costs $5. If you are buying 3 quarts, that means you are multiplying 4 quarts times $5 and multiplying that by 3. When you calculate 5 x 4 x 3 you get a total of $60.
When you multiply $19 x 3 you get a total of $57.
$60 - $57 = $3 so you are saving a total of $3 by buying from the second vendor.
D and then if that doesn't work B. If you have anything else to ask me further about my answer (cause I have got to admit it is quite vague) just ask. Hope this helps :) x