Suppose that $g(x)=f^{-1}(x)$. If $g(-15)=0$, $g(0)=3$, $g(3)=9$ and $g(9)=20$, what is $f(f(9))$?
From \(g(3) = 9\), we know that \(f(9) = 3\).
From \(g(0) = 3\), we know that \(f(3) = 0\).
f(f(9)) = f(3) = 0.
Other informations are useless ones.
+1245 
