$$ \begin{aligned} \frac{x}{4}+2x &= 18&& \text{multiply ALL terms by } \color{blue}{ 4 }. \\[1 em]4 \cdot \frac{x}{4}+4\cdot2x &= 4\cdot18&& \text{cancel out the denominators} \\[1 em]x+8x &= 72&& \text{simplify left side} \\[1 em]9x &= 72&& \text{ divide both sides by $ 9 $ } \\[1 em]x &= \frac{72}{9}&& \\[1 em]x &= 8&& \\[1 em] \end{aligned} $$

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