\begin{cases}15x+6y=3\\-\\15x+3y=3\end{cases}\\\\3y=0\\y=0\\\\15x=3\\x=\frac{1}{5}" alt="\begin{cases}5x+2y=1|*3\\15x+3y=3\end{cases}=>\begin{cases}15x+6y=3\\-\\15x+3y=3\end{cases}\\\\3y=0\\y=0\\\\15x=3\\x=\frac{1}{5}" align="absmiddle" class="latex-formula">
\begin{cases}-15x+20y=120\\+\\15x+9y=-120\end{cases}\\\\29y=0\\y=0\\\\-3x=24\\x=-8" alt="\begin{cases}-3x+4y=24|*5\\5x+3y=-40|*3\end{cases}=>\begin{cases}-15x+20y=120\\+\\15x+9y=-120\end{cases}\\\\29y=0\\y=0\\\\-3x=24\\x=-8" align="absmiddle" class="latex-formula">
\begin{cases}12x-20y=100\\-\\12x-9y=111\end{cases}\\\\-11y=-11\\y=1\\\\3x-5=25\\3x=30\\x=10" alt="\begin{cases}3x-5y=25|*4\\4x-3y=37|*3\end{cases}=>\begin{cases}12x-20y=100\\-\\12x-9y=111\end{cases}\\\\-11y=-11\\y=1\\\\3x-5=25\\3x=30\\x=10" align="absmiddle" class="latex-formula">