Hey sakonpure6.

What exactly is f-g? Is it f(x) - g(x) or is it f(g(x)) or g(f(x))?

If indeed it is f-g = (x-5)(x+3) then (f-g)(-3) is evaluating f-g at x = -3 in which case you can do the substitutions and see the answer (it is one of the options given).