w = 4, l = 12
First, write down what you know.
l = w + 8
2l + 2w = 32
Now substitute (w+8) for l in the 2nd equation.
2(w+8) + 2w = 32
Distribute the 2
2w + 16 + 2w = 32
Subtract 16 from both sides
2w + 2w = 16
Combine the w terms
4w = 16
Divide both sides by 4
w = 4
Now using the l = w+8 expression, substitute the known value for w
l = 4 + 8
l = 12
So w = 4, and l = 12