## Calculus with Applications (10th Edition)

f is increasing in $(-\infty, 3)$ and f is decreasing in $(3,+\infty)$
The function f is undefined when x=3, so 3 is not in the domain of f. $f'(x)=\frac{16}{(9-3x)^{2}}$ $f'(x)>0$ so we have: f is increasing in $(-\infty, 3)$ and f is decreasing in $(3,+\infty)$