To solve for L, you need to isolate/get the variable "L" by itself in the equation:
S = 2HW + 2HL + 2WL Subtract 2HW on both sides
S - 2HW = 2HW - 2HW + 2HL + 2WL
S - 2HW = 2HL + 2WL Take out the "L" in 2HL and 2WL
S - 2HW = L(2H + 2W) Now divide (2H + 2W) to get "L" by itself
[tex]\frac{S-2HW}{2H +2W} =\frac{L(2H+2W)}{2H+2W}[/tex]
[tex]\frac{S-2HW}{2H+2W} =L[/tex]
I think you can stop here, but if you need or want to simplify:
[tex]\frac{S}{2H+2W} -\frac{HW}{H+W} =L[/tex] which looks longer so I don't know if you need to do this
