$$ \begin{aligned} -18 &= -\frac{3}{10}k&& \text{multiply ALL terms by } \color{blue}{ 10 }. \\[1 em]10\cdot(-18) &= -10 \cdot \frac{3}{10}k&& \text{cancel out the denominators} \\[1 em]-180 &= -3k&& \text{ swap the left and right side of the equation } \\[1 em]-3k &= -180&& \text{ divide both sides by $ -3 $ } \\[1 em]k &= \frac{-180}{-3}&& \\[1 em]k &= 60&& \\[1 em] \end{aligned} $$

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