If \(x, y \in (-2, 2)\) and \(xy = -1\), find the minimum value of \(u = \frac{4}{4-x^2} + \frac{9}{9-y^2}\). The original answer is in \(\frac{k}{m}\) format, please give the value of k + m.

Let's think step by step and output the final answer within \boxed{}.
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