College Algebra (11th Edition)

(a) Increasing: $(4,\infty)$ (b) Decreasing: $(-\infty,-1)$ (c) Constant: $(-1,4)$
We see from the graph that $f(x)$ is increasing when $x$ is greater than $4$, decreasing when $x$ is less than $-1$ and constant between $-1$ and $4$.