Since we know that 3 cups make 4 waffles, and we want 12 total waffles, we know that we need to multiply the recipe by 3 in order to have enough ingredients for 12 waffles.
So we multiply 3 cups by 3 (because we need to triple the recipe) and we get:
[tex]3*3=9[/tex]
So we need 9 cups of mix to make 12 waffles.