$$ \begin{aligned} 80+10x\cdot\frac{2}{5}+3-1 &= 0&& \text{multiply ALL terms by } \color{blue}{ 5 }. \\[1 em]5\cdot80+510x\cdot\frac{2}{5}+5\cdot3-5\cdot1 &= 5\cdot0&& \text{cancel out the denominators} \\[1 em]400+20x+15-5 &= 0&& \text{simplify left side} \\[1 em]20x+410 &= 0&& \text{ move the constants to the right } \\[1 em]20x &= -410&& \text{ divide both sides by $ 20 $ } \\[1 em]x &= -\frac{410}{20}&& \\[1 em]x &= -\frac{41}{2}&& \\[1 em] \end{aligned} $$

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