$$\frac{5-a}{a}+\frac{3}{4} = \frac{7}{a}$$

$$ \begin{aligned} \frac{5-a}{a}+\frac{3}{4} &= \frac{7}{a}&& \text{multiply ALL terms by } \color{blue}{ a\cdot4 }. \\[1 em]a\cdot4 \cdot \frac{5-a}{a}+a\cdot4\cdot\frac{3}{4} &= a\cdot4\cdot\frac{7}{a}&& \text{cancel out the denominators} \\[1 em]-4a+20+3a &= 28&& \text{simplify left side} \\[1 em]-a+20 &= 28&& \text{ move 20 to the right } \\[1 em]-a &= 28-20&& \\[1 em]-a &= 8&& \text{switch signs on both sides} \\[1 em]a &= -8&& \\[1 em] \end{aligned} $$

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