These do not involve matrices (or rather they involve 2x2 or 3x3 identity matrices

which are of little consequence) these are vector equations. For the first you

have:

[4x 3y] = [12 -1]

Now equate componets:

4x = 12,

and:

3y = -1.

So x=3, and y=-1/3.

The second is the same exept you have three componets and so three equations.

RonL