Let

be the identity matrix. Then pick whatever matrix you like for

.
Y-4=(x+8) = add4 to both sides of the equation, so y= x+8+4 then add like terms. Y=x+12 final answer.
I would answer but I’m in 6th grade and I don’t know how to
-3x=2x+19
-19 -19
-3x-19=2x
+3x +3x
-19=5x
/5 /5
x=19/5