How much of a 14% solution of iodine should be added to 89 ounces of a 47% iodine solution to get a 29% solution

We have 89 ounces of 47% iodine.
We will add "x" ounces of 14% iodine to get a 29% iodine solution.
89 * .47 + .14x = .29 * (89 + x)
41.83 + .14x = 25.81 + .29x
16.02 = .15x
x = 106.80
So, we must add 106.80 ounces of 14% iodine to get a 29% iodine solution.
(for a total of 195.80 ounces)

Source:
http://www.1728.org/mixture.htm

It would be 15 m how i got the answer: (20x20) + b^2 = (25x25)400 + b^2 = 625625-400=225square that and get 15hope this : )