1)y=5-x 2)x=4-y 3)3y=-1-2x
x-(5-x)=7 3(4-y)-5y=20 y=(-1-2x)/3
x+x-5=7 12-3y-5y=20 3x+5(-1-2x)/3=-2
2x=12 -8y=8 3x-5/3-10x/3=-2
x=6 y=-1 (9x-5-10x)/3=-2/×3
y=5-6=-1 x=4+1=5 -x-5=-6
-x=-1
x=1
y=(-1-2)/3=-3/3=-1
4)x=6-3y
4(6-3y)-9y=3
24-12y-9y=3
24-21y=3
21y=21
y=1
x=6-3=3