inverse functions

Question

Let 

Answer 1

change f(x) to y y = 15 - x

swap the x an y x = 15 - y

solve for y x - 15 = -y

-x + 15 = y or y = 15 - x

rewrite in inverse form f^-1(x) = 15 - x

the graph y = 15 - x is its own mirror image across the line y = x.