To solve the equation \( x - x + 2x + x = 18 \), we first simplify the left-hand side:
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Combine like terms: \[ x - x + 2x + x = 0 + 2x + x = 3x \]
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Now, the equation simplifies to: \[ 3x = 18 \]
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To solve for \( x \), divide both sides by 3: \[ x = \frac{18}{3} = 6 \]
Thus, the solution is: \[ \boxed{6} \]