$$ \begin{aligned} 13 &= 2(y+2)+7y&& \text{simplify right side} \\[1 em]13 &= 2y+4+7y&& \\[1 em]13 &= 9y+4&& \text{ swap the left and right side of the equation } \\[1 em]9y+4 &= 13&& \text{ move 4 to the right } \\[1 em]9y &= 13-4&& \\[1 em]9y &= 9&& \text{ divide both sides by $ 9 $ } \\[1 em]y &= \frac{9}{9}&& \\[1 em]y &= 1&& \\[1 em] \end{aligned} $$

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