$$ \begin{aligned} 2(r+6) &= 4(r+4)&& \text{simplify left and right hand side} \\[1 em]2r+12 &= 4r+16&& \text{move the $ \color{blue}{ 4r } $ to the left side and $ \color{blue}{ 12 }$ to the right} \\[1 em]2r-4r &= 16-12&& \text{simplify left and right hand side} \\[1 em]-2r &= 4&& \text{ divide both sides by $ -2 $ } \\[1 em]r &= -\frac{4}{2}&& \\[1 em]r &= -2&& \\[1 em] \end{aligned} $$

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