$$ \begin{aligned} 9-5x &= 12-(6x+7)&& \text{simplify left and right hand side} \\[1 em]-5x+9 &= 12-6x-7&& \\[1 em]-5x+9 &= -6x+5&& \text{move the $ \color{blue}{ -6x } $ to the left side and $ \color{blue}{ 9 }$ to the right} \\[1 em]-5x+6x &= 5-9&& \text{simplify left and right hand side} \\[1 em]x &= -4&& \\[1 em]x &= -4&& \\[1 em] \end{aligned} $$

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