Find the echelon form of this augmented matrix

Answer:
See the explanation
Step-by-step explanation:
If we want to find the row echelon form of a given matrix, then it should have the following properties:
[tex]\left[\begin{array}{cccc}1&3&-2&400\\-1&-2&-1&-100\\-1&-1&-3&700\end{array}\right][/tex]
Add 1 times the 1st row into 2nd row
[tex]\left[\begin{array}{cccc}1&3&-2&400\\0&1&-3&300\\-1&-1&-3&700\end{array}\right][/tex]
Add 1 time the 1st row into 3rd row
[tex]\left[\begin{array}{cccc}1&3&-2&400\\0&1&-3&300\\0&2&-5&1100\end{array}\right][/tex]
Add -2 times the 2nd row into 3rd row.
[tex]\left[\begin{array}{cccc}1&3&-2&400\\0&1&-3&300\\0&0&1&500\end{array}\right][/tex]