This can be done in two ways
One method is to check the answer options in both f(x) and g(x) and select the one that matches for both.
The second is to form a quadratic equation and solving as such:
f(x) = g(x)
-x² + 4x + 12 = x + 8
x² - 3x - 4 = 0
(x - 4)(x + 1) = 0
x = 4; x = -1
Only x = 4 is given in the options, so the answer is B
