$$ \begin{aligned} 90 &= 10(x+7)&& \text{simplify right side} \\[1 em]90 &= 10x+70&& \text{ swap the left and right side of the equation } \\[1 em]10x+70 &= 90&& \text{ move 70 to the right } \\[1 em]10x &= 90-70&& \\[1 em]10x &= 20&& \text{ divide both sides by $ 10 $ } \\[1 em]x &= \frac{20}{10}&& \\[1 em]x &= 2&& \\[1 em] \end{aligned} $$

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