For the function $f ( x ) = \log _ { x } 2$,
$$f \left( 4 ^ { a } \right) \cdot f ^ { - 1 } \left( \frac { 1 } { 3 } \right) = 6$$
What is the value of a that satisfies this equation?\\
A) $\frac { 1 } { 2 }$\\
B) $\frac { 5 } { 2 }$\\
C) $\frac { 1 } { 3 }$\\
D) $\frac { 2 } { 3 }$\\
E) $\frac { 4 } { 3 }$