Step-by-step explanation:
L+W+L+W=26 so 2L=26–2W and you can find length from the perimeter as L=13−W
LW=42 so L=42/W is the other way to find the length, from the area. Both ways require you to know W, but if you have both pieces of information the two answers for length must be the same 42/W=13−W, and you solve this:
42=13W−W2
W2–13W+42=0
(W−6)(W−7)=0
Either W−6=0 or W−7=0
