Find the Function Value $f ( x ) = \left( \frac { 1 } { 5 } \right) ^ { x }$

Multiple Choice

Find the function value. If the result is irrational, round your answer to the nearest thousandth.
-Let $f ( x ) = \left( \frac { 1 } { 5 } \right) ^ { x }$ . Find $f ( 3 )$ .

A) $\frac { 1 } { 243 }$
B) $\frac { 1 } { 125 }$
C) 125
D) $\frac { 1 } { 15 }$