Instructors led an exercise class from a raised rectangular platform at the front of the room. The width of the platform was (3x- 1) feet and the area was (9x^2 +6x- 3) ft^2. Find the length of this platform. After the exercise studio is remodeled, the area of the platform will be (9x2+ 12x+ 3) ft^2. By how many feet will the width of the platform change?
