$$ \begin{aligned} x+\frac{4}{5} &= -\frac{3}{4}&& \text{multiply ALL terms by } \color{blue}{ 20 }. \\[1 em]20x+20\cdot\frac{4}{5} &= -20\cdot\frac{3}{4}&& \text{cancel out the denominators} \\[1 em]20x+16 &= -15&& \text{ move 16 to the right } \\[1 em]20x &= -15-16&& \\[1 em]20x &= -31&& \text{ divide both sides by $ 20 $ } \\[1 em]x &= -\frac{31}{20}&& \\[1 em] \end{aligned} $$

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