5(3x-1)
(x-3)(x-2)
I don't know if you want working out or an explanation? Or if it's too late, sorry.
There are 16 cups in a gallon. Divide 100 into 16 to get 6.25. You now just multiply 3.12 by 6.25 to get 19.5. Your answer is $19.50. Hope this helps!