\(\dfrac{x}{28}=\dfrac{y}{-14}=\dfrac{-12}{21}\)
=>\(\dfrac{x}{28}=\dfrac{y}{-14}=\dfrac{-4}{7}\)
=>\(\left\{{}\begin{matrix}x=28\cdot\dfrac{\left(-4\right)}{7}=-4\cdot4=-16\\y=\dfrac{\left(-14\right)\cdot\left(-4\right)}{7}=\dfrac{56}{7}=8\end{matrix}\right.\)