Question 912865
{{{(matrix(2,2,3y,12,4,x-1))=(matrix(2,2,x,12,4,8))}}}
Look at each unknown element and match them up.
{{{3y=x}}}
.
.

{{{x-1=8}}}
{{{highlight(x=9)}}}
Then,
{{{3y=9}}}
{{{highlight(y=3)}}}