Precalculus (6th Edition) Blitzer

$x=4,y=6\text{ and }z=3$.
Two matrices are equal if the corresponding elements of the given matrix are equal. That is, \begin{align} & x=4 \\ & 2y=12 \\ \end{align} And, $z=3$ Now $2y=12$ implies that $y=\frac{12}{2}=6$. Hence, $x=4,y=6\text{ and }z=3$.