To solve this problem, we need to figure out how much sugar Grandma needs for her recipe.
We know that the amount of sugar she needs to use is 2/4 cups more than the amount of butter. Therefore, we just need to add 2/4 cups to the amount of butter Grandma used to find the amount of sugar she needs.
Butter = 2 3/4 cups
Sugar = 2 3/4 cups + 2/4 cups = 2 5/4 cups = 3 1/4 cups
Thus, Grandma needs to add 3 1/4 cups of sugar to her mixing bowl.