Answer
$\lim\limits_{x\to4^+}\dfrac{4-x}{x^2-16}=-\dfrac{1}{8}.$
Work Step by Step
$\lim\limits_{x\to4^+}\dfrac{4-x}{x^2-16}=\lim\limits_{x\to4^+}\dfrac{-(x-4)}{(x-4)(x+4)}$
$=\lim\limits_{x\to4^+}\dfrac{-1}{x+4}=-\dfrac{1}{4+4}=-\dfrac{1}{8}.$