To find the inverse of a function, first, let's switch f(x) with y

Now, change all the x's into y's and change all the y's into x's

Now, let's solve this equation in terms of y.
Subtract both sides by 12

Divide both sides by 5

Flip the equation so we have the y on the left

Now, replace the y with


That's your answer. If you need any clarifications, feel free to comment.
Have an awesome day! :)