{y = x - 4
=> 2x+x-4=5 => 3x=9......x=3
{2x + y = 5 y=3-4=-1
________________________________________________
{x+4y=6
{y=-x+3
=> x+4(-x+3)=6
x-4x+12=6
-3x=-6
x=2
y=-2+3=1
y=1
___________________________________________________-
{x+2y=9
{x-y=3 .......x=3+y
3+y+2y=9
3y=6
y=2
x=3+2=5
x=5
_________________________________
{3x-2y=9
{y=2x-7
3x-2(2x-7)=9
3x-4x+14=9
-x=-5
x=5
y=2*5-7=10-7=3
y=3