Ans: $h=\dfrac{15+k^2}{5-k}$
$\begin{array}{rcl}
\dfrac{5}{h+k} & = & \dfrac{k}{h-3}\\
5(h-3) & = & k(h+k) \\
5h-15 & = & hk+k^2 \\
5h-hk & = & k^2+15 \\
h(5-k) & = & k^2+15 \\
h & = & \dfrac{k^2+15}{5-k}
\end{array}$
