Question 720882
Your formula for derivative is not so correct.  You may have just missed remembering the simple formula.  d/dw of {{{(250w-w^2)}}} is d/dw of (250w)- d/dw of (w^2), which is {{{highlight(250 - 2w)}}}. 

NOW, to maximize or minimize the A function, set 250-2w=0, and find w.