$$ \begin{aligned} 2a &= -2+4(a+3)&& \text{simplify right side} \\[1 em]2a &= -2+4a+12&& \\[1 em]2a &= 4a+10&& \text{move the $ \color{blue}{ 4a } $ to the left side} \\[1 em]2a-4a &= 10&& \text{simplify left side} \\[1 em]-2a &= 10&& \text{ divide both sides by $ -2 $ } \\[1 em]a &= -\frac{10}{2}&& \\[1 em]a &= -5&& \\[1 em] \end{aligned} $$

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