Find a Formula for the Inverse of the Function Described $f ( x ) = \frac { x } { 2 } - 20$

Multiple Choice

Find a formula for the inverse of the function described below.
-A size 44 dress in Country C is size 2 in Country D. A function that converts dress sizes in Country C to those in Country D is $f ( x ) = \frac { x } { 2 } - 20$ .

A) $f ^ { - 1 } ( x ) = x + 20$
B) $\mathrm { f } ^ { - 1 } ( \mathrm { x } ) = 2 \mathrm { x } + 20$
C) $f ^ { - 1 } ( x ) = 2 ( x + 20 )$
D) $f ^ { - 1 } ( x ) = 2 ( x - 20 )$