$$ \begin{aligned} \frac{11}{28} &= \frac{x}{30}&& \text{multiply ALL terms by } \color{blue}{ 420 }. \\[1 em]420\cdot\frac{11}{28} &= 420 \cdot \frac{x}{30}&& \text{cancel out the denominators} \\[1 em]165 &= 14x&& \text{ swap the left and right side of the equation } \\[1 em]14x &= 165&& \text{ divide both sides by $ 14 $ } \\[1 em]x &= \frac{165}{14}&& \\[1 em] \end{aligned} $$

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