$$ \begin{aligned} -57 &= 3(y-7)&& \text{simplify right side} \\[1 em]-57 &= 3y-21&& \text{ swap the left and right side of the equation } \\[1 em]3y-21 &= -57&& \text{ move -21 to the right } \\[1 em]3y &= -57+21&& \\[1 em]3y &= -36&& \text{ divide both sides by $ 3 $ } \\[1 em]y &= -\frac{36}{3}&& \\[1 em]y &= -12&& \\[1 em] \end{aligned} $$

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