$$ \begin{aligned} 9x-31 &= 2(2x+2)&& \text{simplify right side} \\[1 em]9x-31 &= 4x+4&& \text{move the $ \color{blue}{ 4x } $ to the left side and $ \color{blue}{ -31 }$ to the right} \\[1 em]9x-4x &= 4+31&& \text{simplify left and right hand side} \\[1 em]5x &= 35&& \text{ divide both sides by $ 5 $ } \\[1 em]x &= \frac{35}{5}&& \\[1 em]x &= 7&& \\[1 em] \end{aligned} $$

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