$$ \begin{aligned} -2 &= 2\cdot(15-4a)&& \text{simplify right side} \\[1 em]-2 &= 30-8a&& \\[1 em]-2 &= -8a+30&& \text{ swap the left and right side of the equation } \\[1 em]-8a+30 &= -2&& \text{ move 30 to the right } \\[1 em]-8a &= -2-30&& \\[1 em]-8a &= -32&& \text{ divide both sides by $ -8 $ } \\[1 em]a &= \frac{-32}{-8}&& \\[1 em]a &= 4&& \\[1 em] \end{aligned} $$

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