Answer
$[x]_B=\begin{bmatrix}
-5/2\\
1/2\\
\end{bmatrix}
$
Work Step by Step
We can calculate the B coordinate vector of x by row reducing the augmented matrix
$\begin{bmatrix}
-3&7&11\\
1&5&0\\
-4&-6&7
\end{bmatrix}
$~$\begin{bmatrix}
1&0&-5/2\\
0&1&1/2\\
0&0&0
\end{bmatrix}$
$[x]_B=\begin{bmatrix}
-5/2\\
1/2\\
\end{bmatrix}
$
