whats the inverse for f(x)=1/3x+2

For ease of typing, I will replace "f(x)" with "y":

To find the inverse of  y = 1/3x + 2:

There are two steps:

Step #1:  interchange x and y:                x  =  1/3y + 2

Step #2:  solve this equation for y:

               -- multiply each term by 3:     3x  =  y + 6

               -- subtract 6 from both sides:  3x - 6  =  y 

So the inverse of             f(x) = 1/3x + 2

is                      f-inverse(x)  = 3x - 6