$$ \begin{aligned} -20 &= \frac{z}{10}-22&& \text{multiply ALL terms by } \color{blue}{ 10 }. \\[1 em]10\cdot(-20) &= 10 \cdot \frac{z}{10}-10\cdot22&& \text{cancel out the denominators} \\[1 em]-200 &= z-220&& \text{ swap the left and right side of the equation } \\[1 em]z-220 &= -200&& \text{ move -220 to the right } \\[1 em]z &= -200+220&& \\[1 em]z &= 20&& \\[1 em]z &= 20&& \\[1 em] \end{aligned} $$

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