#### Answer

$f^{-1}(f^{-1}(0))$ = 4

#### Work Step by Step

First find where f(x) = 0. Since the function is one-to-one, f(5) = 0. Therefore $f^{-1}(f^{-1}(0))$ = $f^{-1}(5)$
Then find where f(x) = 5. Since the function is one-to-one, f(4) = 5. Therefore $f^{-1}(f^{-1}(0))$ = $f^{-1}(5)$ = 4