$$ \begin{aligned} -14 &= -21+\frac{c}{11}&& \text{multiply ALL terms by } \color{blue}{ 11 }. \\[1 em]11\cdot(-14) &= -11\cdot21+11 \cdot \frac{c}{11}&& \text{cancel out the denominators} \\[1 em]-154 &= -231+c&& \text{ swap the left and right side of the equation } \\[1 em]-231+c &= -154&& \text{ move -231 to the right } \\[1 em]c &= -154+231&& \\[1 em]c &= 77&& \\[1 em]c &= 77&& \\[1 em] \end{aligned} $$

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