Answer
$f^{-1}(x)=\frac{4}{x}-2$
See graph.
Work Step by Step
Step 1. $f(x)=\frac{4}{x+2} \Longrightarrow y=\frac{4}{x+2} \Longrightarrow x=\frac{4}{y+2} \Longrightarrow y=\frac{4}{x}-2 \Longrightarrow f^{-1}(x)=\frac{4}{x}-2$
Step 2. Check $f(f^{-1}(x))=\frac{4}{(\frac{4}{x}-2)+2}=x$ and $f^{-1}(f(x))=\frac{4}{\frac{4}{x+2}}-2=x$
Step 3. See graph.