A line $\displaystyle {L}$ has a slope of $\displaystyle {8}$ and passes through the point $\displaystyle {\left({r},-{9}\right)}$. A second line, $\displaystyle {K}$, is perpendicular to $\displaystyle {L}$ at $\displaystyle {\left({s},{t}\right)}$ and passes through point $\displaystyle {\left(-{7},{r}\right)}$, which is not on $\displaystyle {L}$. Express $\displaystyle {s}$ in terms of $\displaystyle {r}$.