[tex]\bf \begin{array}{llll}
18x-y=24&\implies &\quad 18x-y=24\\
9x+4y=-15&\boxed{\times -2}\implies &-18x-8y=30\\
&&--------\\
&&\qquad 0-9y=54
\end{array}\\\\
-----------------------------\\\\
-9y=54\implies y=\cfrac{54}{-9}\implies \boxed{y=-6}
\\\\\\
\textit{now, let's use that "y" in the first equation}
\\\\\\
18x-(-6)=24\implies 18x+6=24\implies 18x=18\implies \boxed{x=1}[/tex]
