If $\left( \frac { 3 ^ { 6 } } { 4 ^ { 4 } } \right) k$ is the term, independent of $x$, in the binomial expansion of $\left( \frac { x } { 4 } - \frac { 12 } { x ^ { 2 } } \right) ^ { 12 }$, then $k$ is equal to
If $\left( \frac { 3 ^ { 6 } } { 4 ^ { 4 } } \right) k$ is the term, independent of $x$, in the binomial expansion of $\left( \frac { x } { 4 } - \frac { 12 } { x ^ { 2 } } \right) ^ { 12 }$, then $k$ is equal to