as you should know, to get the inverse of any expression, we start off by doing a quick switcheroo on the variables and then solve for "y".
[tex]\stackrel{f(x)}{y}=\sqrt{x}-5\implies \stackrel{\textit{quick switcheroo}}{x=\sqrt{y}-5}\implies x+5=\sqrt{y} \implies (x+5)^2=y \\\\\\ \stackrel{F~O~I~L}{(x+5)(x+5)}=y\implies x^2+10x+25=\stackrel{f^{-1}(x)}{y}[/tex]
