The arithmetic mean of $\log _ { 4 } \mathrm { x }$ and $\log _ { 8 } \frac { 1 } { \mathrm { x } }$ is $\frac { 1 } { 2 }$.
Accordingly, what is the value of $\log _ { 16 } \mathbf { x }$?
A) $\frac { 1 } { 2 }$
B) $\frac { 3 } { 2 }$
C) $\frac { 5 } { 2 }$
D) $\frac { 1 } { 4 }$
E) $\frac { 5 } { 4 }$