$$ \begin{aligned} \frac{3}{2}3x\cdot\frac{1}{20} &= -1&& \text{multiply ALL terms by } \color{blue}{ 20 }. \\[1 em]20 \cdot \frac{3}{2}3x\cdot\frac{1}{20} &= 20\cdot(-1)&& \text{cancel out the denominators} \\[1 em]\frac{9}{2}x &= -20&& \text{multiply ALL terms by } \color{blue}{ 2 }. \\[1 em]2 \cdot \frac{9}{2}x &= 2\cdot(-20)&& \text{cancel out the denominators} \\[1 em]9x &= -40&& \text{ divide both sides by $ 9 $ } \\[1 em]x &= -\frac{40}{9}&& \\[1 em] \end{aligned} $$

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