For the functions f(x) = 5x − 3 and g(x) = x + 4, which composition produces the greatest output?

You could actually find the compositions and thus have something to compare.  You haven't shared the list of possible answer choices.

(f+g)(x) = 5x - 3 + x + 4 = 6x + 1

(f-g)(x) = 5x - 3 - x - 4 = 4x - 7

(f*g)(x) = (5x-3)((x+4) = 5x^2 + 20x - 3x - 12 = 5x^2 + 17x - 12

There are also the quotient (f/g)(x) and the compositions f(g(x)) and g(f(x)).

WRite them out.

Then you could arbitrarily select x values, such as 2, 10, etc., subst. them into each composition and determine which output is greatest.