Carol H. answered 09/04/14
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Experienced Mathematics Tutor w/ Master's Degree in Math
My guess would be that the problem is P-2w-2L = 0.
To solve the equation for "P." you would add 2w and 2L to both sides of the equation.
P - 2w - 2L = 0
+2w + 2L = 2w + 2L
P = 2w + 2L which is the formula for the perimeter of a rectangle.
Then, if you are asked to find the perimeter of a rectangle, you replace "w" with its length and "L" with its length, and solve the equation for P.