Answer
$$
\left[ \begin {array}{cccc} 3&2&1&1\\ -1&0&2&0\\7&2&0&0\\-7&-2&0&0\end{array} \right]=0.
$$
Work Step by Step
Given
$$
\left[ \begin {array}{cccc} 3&2&1&1\\ -1&0&2&0\\4&1&-1&0\\3&1&1&0\end{array} \right].
$$
Now, adding the second row to the multiple of the third row by $2$, adding the second row to the multiple of the fourth row by $-2$, we get
$$
\left[ \begin {array}{cccc} 3&2&1&1\\ -1&0&2&0\\7&2&0&0\\-7&-2&0&0\end{array} \right].
$$
Since the fourth row is a multiple of the third row by $-1$, then we have
$$
\left[ \begin {array}{cccc} 3&2&1&1\\ -1&0&2&0\\7&2&0&0\\-7&-2&0&0\end{array} \right]=0.
$$
