\(\dfrac{a}{27}=\dfrac{-45}{b}=\dfrac{-5}{9}\)
\(\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{-5}{9}\cdot27=-15\\b=\dfrac{-45\cdot9}{-5}=81\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a=\dfrac{27.-5}{9}=-15\\b=\dfrac{-45.9}{-5}=81\end{matrix}\right.\)