Answer
$ \left[\begin{array}{rrrr}
-1 & 1 & 2 & 0\\
0 & 4 & 7 & 4\\
1 & -2 & -1 & -1
\end{array}\right]$
Work Step by Step
$\left[\begin{array}{rrrr}
-1 & 1 & 2 & 0\\
3 & 1 & 1 & 4\\
1 & -2 & -1 & -1
\end{array}\right]\quad\overrightarrow{3R_{1}+R_{2}\rightarrow R_{2}}$
$\left[\begin{array}{ccc}
-1 & 1 & 2 & 0\\
3(-1)+3 & 3(1)+1 & 3(2)+1 & 3(0)+4\\
1 & -2 & -1 & -1
\end{array}\right]$
$\rightarrow\left[\begin{array}{rrrr}
-1 & 1 & 2 & 0\\
0 & 4 & 7 & 4\\
1 & -2 & -1 & -1
\end{array}\right]$
