x + 2y - 6 = 0
2y = -x + 6
y = (-1/2)x + 3
2x + 4y - 28 = 0
4y = -2x + 28
y = (-1/2)x + 7
Notice that both lines have slope -1/2.
This means the two lines are parallel.
Parallel lines will have solutions only if one of them is on top of the other (or they are the same lines).
In this case, it is very clear that the two lines are different.
Hence, there is no solution to the two equations.
You can see a sketch here: