$$ \begin{aligned} \frac{12}{13} &= \frac{x}{9}&& \text{multiply ALL terms by } \color{blue}{ 117 }. \\[1 em]117\cdot\frac{12}{13} &= 117 \cdot \frac{x}{9}&& \text{cancel out the denominators} \\[1 em]108 &= 13x&& \text{ swap the left and right side of the equation } \\[1 em]13x &= 108&& \text{ divide both sides by $ 13 $ } \\[1 em]x &= \frac{108}{13}&& \\[1 em] \end{aligned} $$

This page was created using