This is a three-way linear equality. You can turn it into a
system of two equations in two unknowns in 3 ways.
Take your pick of any one of these 3 systems of equations:
or or
They simplify to
or or
Take your pick of which one to solve. You'll get the same answers for
x and y no matter which one you pick to solve. It would be instructive
for you to solve all three to see that you get the same answers.
Edwin