Must be Algebra

Algebra Level 4

\[\begin{cases} x + 7y + 3v + 5u = 16 \\ 8x + 4y + 6v + 2u = -16 \\ 2x + 6y + 4v + 8u = 16 \\ 5x + 3y + 7v + u = -16 \end{cases} \]

Real numbers \(x\), \(y\), \(u\), and \(v\) satisfy the system of equations above. Find \(xyuv\).