For any real number $x$, let $[ x ]$ denote the largest integer less than or equal to $x$. If $$I = \int _ { 0 } ^ { 10 } \left[ \sqrt { \frac { 10 x } { x + 1 } } \right] d x$$ then the value of $9 I$ is $\_\_\_\_$.
For any real number $x$, let $[ x ]$ denote the largest integer less than or equal to $x$. If
$$I = \int _ { 0 } ^ { 10 } \left[ \sqrt { \frac { 10 x } { x + 1 } } \right] d x$$
then the value of $9 I$ is $\_\_\_\_$.