A|B matrix will be given as -
$\begin{bmatrix} 1 &2 &0 &|5 \\ 4& 8 &0 & |12 \\ 3& 6 & 3 & |15 \end{bmatrix}$
After the row-operations - R3->R3-3R1 and
R2->4R1-R2
We obtain the matrix -
$\begin{bmatrix} 1 &2 &0 &|5 \\ 0 & 0& 0& |8\\ 0& 0 & 0 & |0 \end{bmatrix}$
Now since, $Rank(A)\neq Rank(A|B)$
Hence, this is an inconsistent solution, that is, no solution.