Identify the coefficient of \(x^3\) in the polynomial expression obtained by adding \((2x^3 - 4x^2 + 6)\) and \((-5x^3 + 3x^2 - x + 8)\), and then subtracting \((x^3 - x^2 + 2x - 1)\). Let's think step by step and output the final answer within \boxed{}.
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