You have a pool that measures 8 yards by 10 yards. You want to build a deck around all four sides of the pool and you want to increase the total area to 120 square yards. The deck is the same width on both sides forming a perfect rectangle. What is t?

If the width of the deck is represented by w (in yards), the new area will be
  120 = (8 + 2w)*(10 + 2w) = 80 + 36w + 4w^2
  121 = 4w^2 + 36w + 81    (add 1 to make a perfect square)
  11^2 = (2w + 9)^2    (rewrite as squares)
  11 = 2w + 9    (square root)
  2 = 2w    (subtract 9)
  1 = w    (divide by 2)

The deck is 1 yard wide on all sides of the pool.