What is the inverse of the function below ,f(x)=x/4

Call f(x) = y
y = x / 4 - 2   Interchange x and y
x = y/4 - 2     Add 2 to both sides.
(x + 2) = y/4 Multiply by 4
4(x + 2) = y  This is a new y which the question has labeled as r-1(x)
4(x + 2) = r-1(x)

Answer D <<<<< answer. 

It is very instructive to plot both these graphs.  See below. When you do and you add y  = x, the two graphs, the original and the inverse reflect around y  = x. Every inverse does this.

y = x/4 - 2               red
r-1(x) = 4(x + 2)      blue
y = x                       green.

Answer D <<<<<