$\begin{cases}5x-4y=3\\7x-9y=8\end{cases}$
$⇔\begin{cases}35x-28y=21\\35x-45y=40\end{cases}$
$⇔\begin{cases}5x-4y=3\\17y=-19\end{cases}$
$⇔\begin{cases}5x-4y=3\\y=\dfrac{-19}{17}\end{cases}$
$⇔\begin{cases}x=\dfrac{-5}{17}\\y=\dfrac{-19}{17}\end{cases}$