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

Find a formula for the inverse of the function described below.
-A size 4 dress in Country $C$ is size 40 in Country D. A function that converts dress sizes in Country C to those in Country D is $f ( x ) = 2 ( x + 16 )$ .

A) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = \frac { \mathrm { x } } { 2 } + 16$
B) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = \mathrm { x } - 16$
C) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = \frac { \mathrm { x } } { 2 } - 16$
D) $f ^ { - 1 } ( x ) = \frac { x - 16 } { 2 }$