Algebra Level 3

$\frac{x^2}{10}+\frac{28}{x}=\frac{7x}{5}-\frac{40}{x^2}$

The equation above has 4 real roots $$x_1$$, $$x_2$$, $$x_3$$, and $$x_4$$ such that $$x_1<x_2<x_3<x_4$$. Find the value of $$x_1x_3+x_2x_4$$.

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