You can using any equation you want to solve for one of the variables. For instance, if you want to solve for x you turn one of the equations so y is by its self
2x + 3y = 5
4x - y =3
I am going to use 4x - y =3
-y = -4x + 3
y = 4x -3
Now you can substitute 4x - 3 for y in 2x + 3y = 5 and solve for x
2x + 3y = 5
2x + 3(4x - 3) = 5
