$$ \begin{aligned} 8\cdot(3+x) &= x-9&& \text{simplify left side} \\[1 em]24+8x &= x-9&& \\[1 em]8x+24 &= x-9&& \text{move the $ \color{blue}{ x } $ to the left side and $ \color{blue}{ 24 }$ to the right} \\[1 em]8x-x &= -9-24&& \text{simplify left and right hand side} \\[1 em]7x &= -33&& \text{ divide both sides by $ 7 $ } \\[1 em]x &= -\frac{33}{7}&& \\[1 em] \end{aligned} $$

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