\textbf{116.} If $\displaystyle\lim_{x \to 3} \dfrac{x-4}{2x^2+ax+b} = -\infty$, then $a+b$ is equal to: \medskip (1) $-3$ \hfill (2) $3$ \hfill (3) $6$ \hfill (4) $12$ \medskip