\left(
\begin{array}{ccccc}
 1 & 3 & b+4 & | & 8 \\
 0 & -7 & -2b-11 & | & -18 \\
 0 & 0 & b & | & -2b \\
 0 & 0 & 0 & | & 2 (11-b) b
\end{array}
\right)