Question 762704
f(x) = x - 4
g(x) = x^2 + 3

g(f(x)) = g(x - 4) = (x-4)^2 + 3 = x^2 - 8x + 16 + 3 = x^2 - 8x + 19

g(f(x)) = 4 means that x^2 - 8x + 19 = 4 or

{{{x^2 - 8*x + 15 = 0}}}

Using factorizing to solve the quadratic

{{{(x - 5)*(x - 3) = 0}}}

x = 5 or x = 3 are the possible solutions.

:)