Question 652669
Either answer is correct. I usually hedge my answer by giving both as follows;
(1) W = (A - 2L)/2 or
(2) W = A/2 - L 
and let the reader choose the preferred form.
Note a couple of differences that I have from your answers. The first is that you always put the variable that you want, W in this case, on the LEFT side of the equation. Then you read it as W = something, not something = W. The second is that I omit all of the unneccessary parentheses in the answer. This gives a neater appearance to the answer and easier for the reader to "see" the answer. I also have a comment on the given formula. It is the formula for the perimeter of a rectangle, so I'd expect the standard practice of using the variable p, instead of A, which is usually used for area as in
(3) A = lw.
In addition, lower case letters are used for length and width as in
(4) p = 2l + 2w.
(My preference) Answer: w = p/2 - l