Answer:
-2
Step-by-step explanation:
When 2 lines are parallel that means they have the same slope but diffrent y-intercepts. You can also double check this by counting what the slope is on the graph itself, the red line's equation is y=-2x + 2 while the green line's in y = -2x - 4.
Hope this helps!! :)
(Sorry if this is a bit in-depth, I'm just really passionate about people understanding slope)
