[tex]\begin{cases}
x:y=5\text{ rest }9\\
x:(y+3)=4\text{ rest }15
\end{cases}\\\\\\
\begin{cases}
x=5y+9\\
x=4(y+3)+15
\end{cases}\\\\\\
\begin{cases}
x=5y +9\\
x= 4y+12+15
\end{cases}\\\\\\
\begin{cases}
x-5y=9~~~|\cdot(-1)\\
x-4y=27
\end{cases}\\\\\\
\begin{cases}
-x+5y=-9\\
x-4y=27
\end{cases}~\text{(Adunam ecuatiile)}\\\\\\
~~~/~~~~~y=\boxed{18}\\\\
x=4y+27=4\cdot18+27=72+27=\boxed{99}\\\\
\text{Solutia:}\displaystyle\\\\
\boxed{\bf \left{{x=18}\atop{y=99}}\right} [/tex]