For the function f$,$ of $,$ x$,$ equals, $5,$ left parenthesis, x$,$ start superscript, one third, end superscript, minus, $8,$ right parenthesisf $($x$)=5($x $)31(-8),$ find f$,$ to the power minus $1,$ left parenthesis, x$,$ right parenthesisf $-1($x$).$