So, I have the following System of linear equations and I have to determine the set of solutions $\mathcal{L} = (Au)$:
$$\left\{ \begin{array}{ll} a + 2b + c - 3d = 3 \\ -2a + b - 2c + d = -1 \\ 2a + 2c -2d = 2 \\ a + 3b + c -4d = 4 \\ \end{array} \right.$$
If I try to reach row echelon form with the gauß-algorithm I get $c = b - a$ and $d = b - 1$ but what is the solution set now?