Given the expression: s = lw + wh + hl, solve for h.

Minus lw froom both sides
S-lw=wh+hl
S-lw=h(w+l)
divide both sides by (w+l)
=h

Subtract lw from both sides of the equation to give us,
                                     S - lw = wh + hl
Factor out h from the right hand side of the equation,
                                    S - lw = h(w + l)
Divide both side by (w+ l)
                                    (S - lw) / (w + l) = h
Rearranging,
                                      h = (S - lw) / (w + l)