$$ \begin{aligned} 20 &= \frac{5}{9}(x-32)&& \text{simplify right side} \\[1 em]20 &= \frac{5x-160}{9}&& \text{multiply ALL terms by } \color{blue}{ 9 }. \\[1 em]9\cdot20 &= 9 \cdot \frac{5x-160}{9}&& \text{cancel out the denominators} \\[1 em]180 &= 5x-160&& \text{ swap the left and right side of the equation } \\[1 em]5x-160 &= 180&& \text{ move -160 to the right } \\[1 em]5x &= 180+160&& \\[1 em]5x &= 340&& \text{ divide both sides by $ 5 $ } \\[1 em]x &= \frac{340}{5}&& \\[1 em]x &= 68&& \\[1 em] \end{aligned} $$

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