### Instruction: Suppose that $f(x)=4x+5$. What is $f^{-1}(f^{-1}(9))$?### Response: To find $f^{-1}(f^{-1}(9))$, I need to first find $f^{-1}(9)$ and then apply $f^{-1}$ to that result.
To find $f^{-1}(9)$, I need to undo what $f$ does to $x$.
That means I need to subtract $5$ from $9$ and then divide by $4$.
So, $f^{-1}(9) = \frac{9-5}{4} = 1$.
Now, to find $f^{-1}(f^{-1}(9))$, I need to apply $f^{-1}$ to $1$.
That means I need to subtract $5$ from $1$ and then divide by $4$.
So, $f^{-1}(f^{-1}(9)) = \frac{1-5}{4} = -1$.