f(x) = -5x - 4
Replace f(x) with x and x with y
x = -5y - 4
Let's solve for y. Add 4 to both sides.
x + 4 = -5y
Divide both sides by -5
-1/5x - 4/5 = y
Replace y with f^-1(x)
f^-1(x) = -1/5x - 4/5 is the inverse
