$$ \begin{aligned} x &= \frac{1}{2}x+20&& \text{multiply ALL terms by } \color{blue}{ 2 }. \\[1 em]2x &= 2 \cdot \frac{1}{2}x+2\cdot20&& \text{cancel out the denominators} \\[1 em]2x &= x+40&& \text{move the $ \color{blue}{ x } $ to the left side} \\[1 em]2x-x &= 40&& \text{simplify left side} \\[1 em]x &= 40&& \\[1 em]x &= 40&& \\[1 em] \end{aligned} $$

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