Chapter 9 - Section 9.2 - Solving Systems of Equations Using Matrices - Exercise Set - Page 648: 30

B

Matrix A doesn't account for the fact that the equation is $x-6=0$. Also, this matrix makes the $-6$ the coefficient for $y$, but $y$ is not in the equation. Matrix C sets the first equation equal to $-6$; however, the equation is $x-6=0$. Thus, $x=6$.