$$x = 150-2\cdot(120-2x)$$

$$ \begin{aligned} x &= 150-2\cdot(120-2x)&& \text{simplify right side} \\[1 em]x &= 150-(240-4x)&& \\[1 em]x &= 150-240+4x&& \\[1 em]x &= 4x-90&& \text{move the $ \color{blue}{ 4x } $ to the left side} \\[1 em]x-4x &= -90&& \text{simplify left side} \\[1 em]-3x &= -90&& \text{ divide both sides by $ -3 $ } \\[1 em]x &= \frac{-90}{-3}&& \\[1 em]x &= 30&& \\[1 em] \end{aligned} $$

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