$$ \begin{aligned} \frac{1}{3}x+x &= 24&& \text{multiply ALL terms by } \color{blue}{ 3 }. \\[1 em]3 \cdot \frac{1}{3}x+3x &= 3\cdot24&& \text{cancel out the denominators} \\[1 em]x+3x &= 72&& \text{simplify left side} \\[1 em]4x &= 72&& \text{ divide both sides by $ 4 $ } \\[1 em]x &= \frac{72}{4}&& \\[1 em]x &= 18&& \\[1 em] \end{aligned} $$

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