Suppose that g(x)=f^{-1}(x). If g(-15)=0, g(0)=3, g(3)=9 and g(9)=20, what is f(f(9))?

Suppose that g(x)  =  f^{-1}(x). If g(-15)=0, g(0)=3, g(3)=9 and g(9)=20, what is f(f(9))?

f(x)  must be the inverse  of  f^-1(x)

And   g(x)  = f^-1(x)    

So...the points  ( -15,0)   (0, 3) and   ( 3,9)    are on  g(x)  and  f^-1(x)

Which means  that the points  ( 0, -15)    (3, 0 )  and  ( 9,3)   are  on f(x)

So

f(9)  = 3

And

f ( f (9))   =  f(3)   =   0