If the Function $f ( x ) = \frac { x + 9 } { 5 }$

Multiple Choice

If the function $f ( x ) = \frac { x + 9 } { 5 }$ is one-to-one, find its inverse.

A) $f ^ { - 1 } ( x ) = \frac { 5 } { x + 9 }$
B) $f ^ { - 1 } ( x ) = 5 x - 9$
C) $f ^ { - 1 } ( x ) = 5 x + 9$
D) not one-to-one