The owners of the rectangular swimming pool in the illustration want to surround the pool with a crushed-stone border of uniform width. They have enough stone to cover 78 square meters. How wide should they make the border? (Hint: The area of the larger rectangle minus the area of the smaller is the area of the border. Assume a = 29 m and b = 8 m.

a+2w b+2w outside area

a and b = inside area