$$ \begin{aligned} 10 &= 2 \cdot \frac{x}{30}&& \text{multiply ALL terms by } \color{blue}{ 30 }. \\[1 em]30\cdot10 &= 30\cdot2 \cdot \frac{x}{30}&& \text{cancel out the denominators} \\[1 em]300 &= 2x&& \text{ swap the left and right side of the equation } \\[1 em]2x &= 300&& \text{ divide both sides by $ 2 $ } \\[1 em]x &= \frac{300}{2}&& \\[1 em]x &= 150&& \\[1 em] \end{aligned} $$

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