[tex]\bf \begin{array}{llcll}
3x-y=7&&3x-y=7\\
x+y=-11&\boxed{\times -3}\implies &-3x-3y=33\\
&&-------\\
&&0-4y=40
\end{array}\\\\
y=\cfrac{40}{-4}\implies y=-10\\\\
-----------------------------\\\\
\begin{array}{cllll}
x-7y=-9\\
-x+8y=10\\
--------\\
0+y=1
\end{array}\\\\
-----------------------------\\\\
\begin{array}{llcll}
7x+y=14&\boxed{\times -3}\implies &-21x-3y=-42\\
8x+3y=16&&8x+3y=16\\
&&--------\\
&&-13x+0=-26
\end{array}
\\\\
x=\cfrac{-26}{-13}\implies x=2[/tex]
notice, the 2nd one, had a x and -x, so, we don't have to multiply anything there, just cancel those two out
