$$-\frac{18}{5} = \frac{1}{2}k$$

$$ \begin{aligned} -\frac{18}{5} &= \frac{1}{2}k&& \text{multiply ALL terms by } \color{blue}{ 10 }. \\[1 em]-10\cdot\frac{18}{5} &= 10 \cdot \frac{1}{2}k&& \text{cancel out the denominators} \\[1 em]-36 &= 5k&& \text{ swap the left and right side of the equation } \\[1 em]5k &= -36&& \text{ divide both sides by $ 5 $ } \\[1 em]k &= -\frac{36}{5}&& \\[1 em] \end{aligned} $$

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