$$ \begin{aligned} -3+3 \cdot \frac{x}{4} &= 0&& \text{multiply ALL terms by } \color{blue}{ 4 }. \\[1 em]-4\cdot3+4\cdot3 \cdot \frac{x}{4} &= 4\cdot0&& \text{cancel out the denominators} \\[1 em]-12+3x &= 0&& \text{ move the constants to the right } \\[1 em]3x &= 12&& \text{ divide both sides by $ 3 $ } \\[1 em]x &= \frac{12}{3}&& \\[1 em]x &= 4&& \\[1 em] \end{aligned} $$

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