Let be "x" the amount of cups of mayonnaise that he will need to make 1 cup of tuna fish salad and "y" the amount of cups of mayonnaise that he will need to make 9 times the recipe.
Knowing that it takes of mayonnaise to make of tuna fish salad, we can set up the following proportion:
Solving for "x", you get:
So "y" will be:
Substituting the value of "x" into the equation, we get: