$$ \begin{aligned} 42 &= \frac{7}{3}x&& \text{multiply ALL terms by } \color{blue}{ 3 }. \\[1 em]3\cdot42 &= 3 \cdot \frac{7}{3}x&& \text{cancel out the denominators} \\[1 em]126 &= 7x&& \text{ swap the left and right side of the equation } \\[1 em]7x &= 126&& \text{ divide both sides by $ 7 $ } \\[1 em]x &= \frac{126}{7}&& \\[1 em]x &= 18&& \\[1 em] \end{aligned} $$

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