The answer is 27 cups of onion.
Let x be the multiplier.
From the ratio: green pepper : onion : tomato = 1 : 3 : 9; we can conclude that for salsa we need 1x + 3x + 9x.
If we want 117 cups of salsa, then the equation is as following 1x + 3x + 9x = 117;
From here, we can calculate x: 13x = 117; x = 117/13; x = 9.
Since we need 3x onion and x = 9, it is easy to calculate number of cups of onion: 3x = 3 * 9 = 27.
Thus, for the recipe, 27 cups of onion are needed.
