The question is incomplete. It comes with a set of answer choices.
These are the answer choices:
Alex observes it as 10 m/s, and his friend observes it as less than 10 m/s.
Alex observes it as less than 10 m/s, and his friend observes it as 10 m/s.
Both Alex and his friend observe it as 10 m/s.
Both Alex and his friend observe it as less than 10 m/s.
Answer: Both Alex and his friend observe it as 10 m/s.
Justification:
1) The speed is relative to the frame of reference.
2) It is said that the both Alex and his friend are standing still.
3) Then, the speed they both see is the same, 10 m/s, respect the Earth (where they are standing still).
Of course, Alex is watching the ball moving away and his friend is seing it approaching, but it is not relevant for the question, as it deals with the speed which is only about magnitude, not direction.
