Find the Intervals on Which the Function Is Increasing and the Intervals

Multiple Choice

Find the intervals on which the function is increasing and the intervals on which the function is decreasing.
- $$f ( x ) = - \frac { 1 } { 3 } x ^ { 2 } + 7 x - 8$$

A) Increasing on $\left( - \infty , \frac { 21 } { 11 } \right)$ ; decreasing on $\left( \frac { 21 } { 11 } , \infty \right)$
B) Increasing on $\left( - \infty , \frac { 21 } { 2 } \right)$ ; decreasing on $\left( \frac { 21 } { 2 } , \infty \right)$
C) Increasing on $\left( - \infty , \frac { 21 } { 13 } \right) ;$ decreasing on $\left( \frac { 21 } { 13 } , \infty \right)$
D) Increasing on $\left( - \infty , \frac { 21 } { 4 } \right) ;$ decreasing on $\left( \frac { 21 } { 4 } , \infty \right)$