Answer
See below
Work Step by Step
We obtain $B=\begin{bmatrix}
b_1,b_2
\end{bmatrix}=\begin{bmatrix}
2 & 5 & 0 & 1\\-1 &7&0&2\\4&-6&0&3
\end{bmatrix}$
The row vectors of $B$ is:
$a_1=\begin{bmatrix}
2 &5&0&1
\end{bmatrix}\\
a_2=\begin{bmatrix}
-1&7&0&2
\end{bmatrix}\\
a_3=\begin{bmatrix}
4&-6 &0&3
\end{bmatrix}$
