Hi there!
Since we are dealing with such large distances, we can approximate.
Recall that the equation for speed is:
displacement / time = velocity
OR:
d/t = v
Begin by converting one hour to seconds:
1 hr = 3600 sec
Now, we can solve for velocity:
(-2.0 × 10⁷) / 3600 = -5555.6 m/s ⇒ D: -5.55 × 10³ m/s