Easter Math Puzzle

There is no hint

x + y + z = 4
x + 2y + 4z = 12
2x - 3y - z = 4

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x = 2
y = -1
z = 3

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result => 2 - 2 x (-1) x 3 => 2 + 2 x 3 => 2 + 6 => 8

Final answer: 8

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Solved 139