Answer:
Q = -6
Explanation:
We assume your equations are ...
If you multiply the first equation by 2, it becomes ...
2x -6y = 8
In order for the solution to the system to match the first line, the second equation must be dependent on the first. That is, the second equation must match the one we just found. In order for that to be the case, we must have ...
2x -6y = 8
2x +Qy = 8 ⇒ Q = -6