Answer
$x=-10,\quad y=10$
Work Step by Step
$A=\left[\begin{array}{ll}
3 & 4\\
7 & 9
\end{array}\right],\qquad B=\left[\begin{array}{l}
10\\
20
\end{array}\right],\quad X=A^{-1}B$
$ad-bc=3(9)-(4)(7)=-1\neq 0$
$A^{-1}=(-1)\cdot\left[\begin{array}{ll}
9 & -4\\
-7 & 3
\end{array}\right]$
$A^{-1}=\left[\begin{array}{ll}
-9 & 4\\
7 & -3
\end{array}\right]$
$X=A^{-1}B$
$X=\left[\begin{array}{ll}
-9 & 4\\
7 & -3
\end{array}\right]\left[\begin{array}{l}
10\\
20
\end{array}\right]=\left[\begin{array}{l}
-9(10)+4(20)\\
7(10)-3(20)
\end{array}\right]=\left[\begin{array}{l}
-10\\
10
\end{array}\right]$
$x=-10,\quad y=10$
