Answer
$\left\{\begin{array}{rrrrrrr}
x & +y & +6z & +w & =-2\\
x & -5y & & & =9
\end{array}\right.$
Work Step by Step
The product of the two matrices on the LHS is a 2$\times$1 matrix:
$\left[\begin{array}{l}
0x+y+6z+w\\
x-5y+0z+0w
\end{array}\right].\qquad $Equating it to $\left[\begin{array}{l}
-2\\
9
\end{array}\right]$ leads to
the system of equations
$\left\{\begin{array}{lllll}
x & +y & +6z & +w & =-2\\
x & -5y & & & =9
\end{array}\right.$
