$$ \begin{aligned} 7-\frac{28}{4}+3x\cdot6 &= 0&& \text{multiply ALL terms by } \color{blue}{ 4 }. \\[1 em]4\cdot7-4\cdot\frac{28}{4}+43x\cdot6 &= 4\cdot0&& \text{cancel out the denominators} \\[1 em]28-28+72x &= 0&& \text{simplify left side} \\[1 em]28-28+72x &= 0&& \\[1 em]72x &= 0&& \text{ divide both sides by $ 72 $ } \\[1 em]x &= \frac{0}{72}&& \\[1 em]x &= 0&& \\[1 em] \end{aligned} $$

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