Answer
$4$, or (B)
Work Step by Step
X-intercept: x values such that $y = 0$, so set this function equal to 0. $y = x^2-4x+12 = 0$
Solve by factoring. Find two numbers that add to -4 and multiply to -12.
-6 and 2: -6*2 = -12, -6+2 = -4.
$x^2 -4x+12 = 0, (x-6)(x+2) = 0$ (check the answer by FOIL-ing)
$x = 6, x = -2$
The sum of the x-intercepts: $6-2 = 4$
