1st equation: y = 3x + 6
2nd equation: 3x - y = 6
Substitute the y in the 2nd equation by its value in the 1st equation.
y = 3x + 6
3x - y = 6
3x - (3x + 6) = 6
3x - 3x - 6 = 6
-6 = 6 NOT A SOLUTION
3x -y = 6
3x = 6 + y
x = (6 + y)/3
y = 3x + 6
y = 3((6+y)/3) + 6
y = 6 + y + 6
y = 12 + y
y - y = 12
0 = 12 NOT A SOLUTION
