Answer:
(P-2W)/2=L
Step-by-step explanation:
In this case, you have three incognita, you can't put a number on any of them if you don't know the real value.
The only thing you can do here is to let alone the L depending on the other incognitas.
To do this just use math to let L alone and you'll find:
P=2L + 2W
P-2W=2L
(P-2W)/2=L
And that's it.
