Compute the Exact Value of the Function for the Given $f ( x ) = 3 ^ { 1 - x }$

Compute the exact value of the function for the given x-value without using a calculator.
- $f ( x ) = 3 ^ { 1 - x }$ for $x = 4$

A) $- 9$
B) 27
C) $\frac { 1 } { 27 }$
D) $\frac { 1 } { 9 }$