Matrix

$\begin{bmatrix} 2x-y & 5 \\ 3 & y \end{bmatrix} = \begin{bmatrix} 8 & 5 \\ 3 & 6 \end{bmatrix},$

here, $2x-y=8$ ....(i) and $y=6$ ..........(ii)

so, $2x-6=8$

or, $2x=14$

or, $x=7$

or, $12x= 12\times 7$

or, $12x= \large\boxed{84}$

$\begin{bmatrix}2x-y & 5 \\3 & y \end{bmatrix}=\begin{bmatrix} 8 & 5 \\ 3 & 6 \end{bmatrix}$

we get, $2x-y=8$ .....................[1]

and $y=6$ ................................[2]

by doing [1]+[2], we get,

$2x-y+y=8+6$

or, $x=7$

or, $12x=7 \times 12=84$

$\begin{bmatrix} 2x-y & 5 \\ 3 & y \end{bmatrix} = \begin{bmatrix} 8 & 5 \\ 3 & 6 \end{bmatrix},$

then $2x-y = 8$ and $y=6$ ;

Solving for $x$ by plugging in $y \implies x=7 \implies 12x= 12\times 7 = 84$