$$ \begin{aligned} 2+1-3\cdot\frac{2}{7} &= x&& \text{multiply ALL terms by } \color{blue}{ 7 }. \\[1 em]7\cdot2+7\cdot1-7\cdot3\cdot\frac{2}{7} &= 7x&& \text{cancel out the denominators} \\[1 em]14+7-6 &= 7x&& \text{simplify left side} \\[1 em]15 &= 7x&& \text{ swap the left and right side of the equation } \\[1 em]7x &= 15&& \text{ divide both sides by $ 7 $ } \\[1 em]x &= \frac{15}{7}&& \\[1 em] \end{aligned} $$

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