Elementary Linear Algebra 7th Edition

The augmented matrix is given by $$\left[ \begin {array}{cccc} 1&2&1&8\\ -3&-6&-3&-21 \end {array} \right] .$$ Multiply the first row by $3$ and adding it the second row , we get $$\left[ \begin {array}{ccccc} 1&2&1&8\\ 0&0&0&3\end {array} \right].$$ Now, the crossposting system is given by $$\begin{array}{l} x+2y+z&=8 \\ 0 z&=3. \end{array}$$ The above system is inconsistent and has no solutions.