$$ \begin{aligned} x &= 450-2 \cdot \frac{x}{10}&& \text{multiply ALL terms by } \color{blue}{ 10 }. \\[1 em]10x &= 10\cdot450-10\cdot2 \cdot \frac{x}{10}&& \text{cancel out the denominators} \\[1 em]10x &= 4500-2x&& \text{move the $ \color{blue}{ -2x } $ to the left side} \\[1 em]10x+2x &= 4500&& \text{simplify left side} \\[1 em]12x &= 4500&& \text{ divide both sides by $ 12 $ } \\[1 em]x &= \frac{4500}{12}&& \\[1 em]x &= 375&& \\[1 em] \end{aligned} $$

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