Identify the Open Intervals on Which the Function $y = 9 x - 18 \cos x , 0 < x < 2 \pi \text { is }$

Multiple Choice

Identify the open intervals on which the function $y = 9 x - 18 \cos x , 0 < x < 2 \pi \text { is }$ increasing or decreasing.

A) increasing on $\left( \frac { 7 \pi } { 6 } , \frac { 11 \pi } { 6 } \right) ;$ decreasing on $\left( 0 , \frac { 7 \pi } { 6 } \right)$ and $\left( \frac { 11 \pi } { 6 } , 2 \pi \right)$
B) increasing on $\left( 0 , \frac { 11 \pi } { 6 } \right)$ and $\left( \frac { 7 \pi } { 6 } , 2 \pi \right)$ ; decreasing on $\left( 0 , \frac { 7 \pi } { 6 } \right)$
C) increasing on $\left( 0 , \frac { 7 \pi } { 6 } \right)$ and $\left( \frac { 11 \pi } { 6 } , 2 \pi \right)$ ; decreasing on $\left( \frac { 7 \pi } { 6 } , \frac { 11 \pi } { 6 } \right)$
D) increasing on $\left( 0 , \frac { 7 \pi } { 6 } \right)$ and $\left( \frac { 5 \pi } { 6 } , 2 \pi \right)$ ; decreasing on $\left( \frac { 7 \pi } { 6 } , \frac { 5 \pi } { 6 } \right)$
E) increasing on $\left( \frac { 7 \pi } { 6 } , \frac { 5 \pi } { 6 } \right)$ and $\left( \frac { 5 \pi } { 6 } , 2 \pi \right)$ ; decreasing on $\left( \frac { 5 \pi } { 6 } , \frac { 11 \pi } { 6 } \right)$