\[(a + 4)x \leq a^{2} - 16\]
\[(a + 4)x \leq (a - 4)(a + 4)\]
\[a = - 4 \Longrightarrow 0 \cdot x \leq 0,\ \ \ ( - \infty; + \infty)\]
\[a < - 4 \Longrightarrow x \geq a - 4\]
\[a > - 4 \Longrightarrow x \leq a - 4\]