$$x = \frac{4}{5}(x+10)$$

$$ \begin{aligned} x &= \frac{4}{5}(x+10)&& \text{simplify right side} \\[1 em]x &= \frac{4x+40}{5}&& \text{multiply ALL terms by } \color{blue}{ 5 }. \\[1 em]5x &= 5 \cdot \frac{4x+40}{5}&& \text{cancel out the denominators} \\[1 em]5x &= 4x+40&& \text{move the $ \color{blue}{ 4x } $ to the left side} \\[1 em]5x-4x &= 40&& \text{simplify left side} \\[1 em]x &= 40&& \\[1 em]x &= 40&& \\[1 em] \end{aligned} $$

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