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The equation is
    x^2 + (x+7)^2 = 73^2.
Instead of formal solving, I look into the table of the Pythagorean triples
https://en.wikipedia.org/wiki/Pythagorean_triple
and I quickly find there the triple  (48,55,73)  with the diagonal of 73, which satisfies all conditions.     ANSWER
Solved.