3 Answers

You know what?   I don't think you can solve that equation and get any real numbers in there.  You could just plug in some number and see if you can work it backwards.

 L =  P - 2W/2

Let L = 40    40 = P - 2W/2
40(2) = P - 2W/2 x 2
80 = P - 2W
Now what:  W can be pretty much any number.  Whatever it is doubled, you just add 80 to it and that is P.  Here are two scenarios for W:

W = 37          80 =  P - 37(2)       80 = P - 74       80 + 74 = P -74 + 74     154 = P
W = -12         80 = P - (-12)2       80 = P + 24       80 - 24 = P + 24 - 24         56 = P 

If the numerator is P-2W and the denominator is 2 (that means, P-2W is divided by 2), then

L = (P-2W)/2 = P/2 - 2W/2 = P/2 - W

If the numerator is 2W and the denominator is 2 (that means, 2W/2 is subtracted from P), then

L = P - 2W/2 = P - W

Please let me know if you have any questions.

You want to get P by itself. First multiply by 2 gives you 2L=p-2w then you want p isolated, so add 2w to both sides (cancelling out on the other) gives you 2L+2w=P