Let $a = 3 \sqrt { 2 }$ and $b = \frac { 1 } { 5 ^ { 1 / 6 } \sqrt { 6 } }$. If $x , y \in \mathbb { R }$ are such that
$$\begin{aligned} & 3 x + 2 y = \log _ { a } ( 18 ) ^ { \frac { 5 } { 4 } } \\ & 2 x - y = \log _ { b } ( \sqrt { 1080 } ) \end{aligned}$$
then $4 x + 5 y$ is equal to $\_\_\_\_$ .