##### Item1.2.5.2.d

The reduced row echleon form is

\begin{equation*} \left[ \begin{array}{rrrr|r} 1 \amp 0 \amp 0 \amp 1 \amp 0 \\ 0 \amp 1 \amp 0 \amp 0 \amp 3 \\ 0 \amp 0 \amp 1 \amp 0 \amp -1 \\ \end{array} \right]\text{,} \end{equation*}and there are infinitely many solutions.