5. The reason you would need 5 cups is simple. For 48 cookies you need 3 cups of flour meaning that 48/3 is 16 cookies PER CUP. In order to find out how many cups is needed for 80 in simple. You found out that 1 cup of flour makes 16 cookies. Divide 80 by 16 (80/16) and you get 5. You would need 5 cups of flour.