Answer:
I'm pretty sure it's +(-6).
Explanation:
Basically for these, you find the slope. The slope equation is y1-y2/x1-x2.
Pick two points.
I'll just do (1,15) and (2,9).
15-9/1-2 = 6/-1 = -6.
I don't know if you were taught it this way, but my math teacher always told us that the rate of change had to be positive.
So you'd say the rate of change is +(-6), not -6.
Hope that sorta helped lol