Question 830868
The perimeter is a fence around.  It requires 2 lengths of fence + 2 widths of fence. (P = 2L + 2W)
You're given the following information:
P = 80
L = W + 4
Substitute the value for L in the original equation:
P (80) = 2(W+4) + 2W
Distribute
80 = 2W + 8 + 2W
Add the Ws
80 = 4W + 8
Subtract 8 from each side
72 = 4W
Divide each side by 4
18 = W
.
Since you know the width is 18, you can find the length by adding 4.  18+4=22
Let's make certain by putting in the values:
2(22) + 2(18) = 80
44 + 36 does indeed equal 80.