Question: Find x and y so

\[\left[ \begin{matrix} x & -1 \\ 1 & 0 \\ \end{matrix} \right]\left[ \begin{matrix} 2 & 1 \\ 4 & 1 \\ \end{matrix} \right]=\left[ \begin{matrix} y & 7 \\ y & -6 \\ \end{matrix} \right]\]