Answer: [tex]\bold{L=\dfrac{S-2WH}{2W+2H}}[/tex]
Step-by-step explanation:
[tex]S=(2W+2H)L+2WH\\\\\\\underline{\text{Subtract 2WH from both sides:}}\\S-2WH=(2W+2H)L\\\\\\\underline{\text{Divide both sides by (2W + 2H):}}\\\\\dfrac{S-2WH}{2W+2H}=L[/tex]