3x-4y=13
x=9-y
3×(9-y)-4y=13
27-3y-4y=13
-7y=13-27
-7y=-14
y=-4÷-7
y=2
x+2=9
x=9-2
x=7
3×7-4×2=13
21-8=13
13=13
2+7=9
x=7; y=2
3x-4y=13
x=9-y
3×(9-y)-4y=13
27-3y-4y=13
-7y=13-27
-7y=-14
y=-4÷-7
y=2
x+2=9
x=9-2
x=7
3×7-4×2=13
21-8=13
13=13
2+7=9
x=7; y=2