If the function f(x) = mx + b has an inverse function, which statement must be true?

F(x) = mx + b is just equal to the equation
y = mx + b

In order for us to get the inverse function, then we can interchange x to y and y to x
y = mx + b
x = my + b

Then we need to find y
x = my + b
-my = -x + b
my = x - b
y = (x-b) / m
f(x) = (x - b) / m