Find a Formula for the Inverse of the Function Described $C$

Multiple Choice

Find a formula for the inverse of the function described below.
-A size 4 dress in Country $C$ is size 42 in Country D. A function that converts dress sizes in Country $C$ to those in Country $D$ is $f ( x ) = x + 38$ .

A) $f ^ { - 1 } ( x ) = x - 38$
B) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = \frac { \mathrm { x } } { - 38 }$
C) $f ^ { - 1 } ( x ) = x + 38$
D) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = \frac { \mathrm { x } } { 38 }$