Inverse of f (x) = -5x+15

f (x) = - 5x - 15

Let y = f (x)

y = - 5x - 15

Switch the x and y places, and solve for y:

x = - 5y - 15

-5y = x + 15

y = (x + 15) / -5

y = - (x/5) - 3

So the inverse of : f (x) = - 5x - 15 is

-x/5 - 3