Wilson cuts rectangular mats for picture frames. The area of the mat before it is cut is represented by the function M(x) = 4.5x^2 + 17x + 16. The area that is cut out and removed from the middle of the mat is represented by the function N(x) = x^2 + 6x. If x is the width of the portion of the mat that is cut out, which function best describes A(x), the area of the cut mat?