$$ \begin{aligned} \frac{9}{d} &= 27&& \text{multiply ALL terms by } \color{blue}{ d }. \\[1 em]d\cdot\frac{9}{d} &= d\cdot27&& \text{cancel out the denominators} \\[1 em]9 &= 27d&& \text{ swap the left and right side of the equation } \\[1 em]27d &= 9&& \text{ divide both sides by $ 27 $ } \\[1 em]d &= \frac{9}{27}&& \\[1 em]d &= \frac{1}{3}&& \\[1 em] \end{aligned} $$

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