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Answer
(x+y)(x-y) = 225
225 = 3^2 * 5^2
Number of factors = 3*3 = 9 = 225*1, 45*5, 25*9, 75*3, 15*15
x+y = 225 , x-y = 1 -> 1 solution pair. Similarly x+y = 1, x-y = 225 -> 1 solution pair
15*15 gives only 1 solution pair
Total number of pairs = 4*2 + 1 = 9
