Use Composition to Show That the Pair of Functions Are $f ( x ) = 3 x + 7 , f ^ { - 1 } ( x ) = \frac { x - 7 } { 3 }$

Use composition to show that the pair of functions are inverses. $f ( x ) = 3 x + 7 , f ^ { - 1 } ( x ) = \frac { x - 7 } { 3 }$