Answer:
Explanation:
The change must be 30 - - 40 which means it came in a 30 meters / second and went out in the opposite direction at 40 meters / second
The change is 70 m/sec.
You could show it to be - 70 meters per second as well. That's done by making the outgoing direction minus.
Delta v = vf - vi.
Now it depends on which way you define vf and vi.
