You don't have to worry about the rectangle or the perimeter.
They're just giving you an equation and asking you to 'solve' it for 'W' ...
massage it around so that 'W' is all by itself on one side. I'm pretty sure
you've done this kind of thing before.
the original equation P = 2 L + 2 W
Subtract 2L
from each side: P - 2 L = 2 W
Divide each side by 2 : (P - 2 L) / 2 = W
Choice - (2) says that.