Question

How to solve for W in A=2(L+W) equation

Answer 1

A  = 2(L + W)
Divide both sides by 2.
A / 2 = L + W
A / 2 - L  =  W

W = A/2 - L

Answer 2

$A = 2(L+W)\\\frac{A}{2}= l + W \\W = \frac{A}{2} - l$

I hope that helps :)