Question 17442
s = 2wl + 2lh + 2wh
subtract 2wh from both sides
s - 2wh = 2wl + 2lh
now factor out l on the right hand side of the equation
s - 2wh = l(2w+2h)
now divide both sides by (2w+2h)
{{{(s - 2wh)/(2w+2h)}}} = l