$$y+9\cdot\frac{1}{2} = 4$$

$$ \begin{aligned} y+9\cdot\frac{1}{2} &= 4&& \text{multiply ALL terms by } \color{blue}{ 2 }. \\[1 em]2y+2\cdot9\cdot\frac{1}{2} &= 2\cdot4&& \text{cancel out the denominators} \\[1 em]2y+9 &= 8&& \text{ move 9 to the right } \\[1 em]2y &= 8-9&& \\[1 em]2y &= -1&& \text{ divide both sides by $ 2 $ } \\[1 em]y &= -\frac{1}{2}&& \\[1 em] \end{aligned} $$

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