$$4+5 \cdot \frac{7-x}{9} = -1$$

$$ \begin{aligned} 4+5 \cdot \frac{7-x}{9} &= -1&& \text{multiply ALL terms by } \color{blue}{ 9 }. \\[1 em]9\cdot4+9\cdot5 \cdot \frac{7-x}{9} &= 9\cdot(-1)&& \text{cancel out the denominators} \\[1 em]36-5x+35 &= -9&& \text{simplify left side} \\[1 em]-5x+71 &= -9&& \text{ move 71 to the right } \\[1 em]-5x &= -9-71&& \\[1 em]-5x &= -80&& \text{ divide both sides by $ -5 $ } \\[1 em]x &= \frac{-80}{-5}&& \\[1 em]x &= 16&& \\[1 em] \end{aligned} $$

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