Refer to figure.
The navigation lights should be:

• Red on the Left (port) side (110° coverage)
• Green on the Right (starboard) side (110° coverage)
• White at the Rear of the aircraft (140° coverage), which means 70° on each side of the fuselage centerline

A red navigation light signifies the left wingtip of another aircraft. In this question, the term 'on a constant relative bearing' is the key phrase to determine the answer. A constant relative bearing means that the angle between your aircraft's heading and the position of the other aircraft is not changing over time, and the red light stays in the same spot in your window.

• If the other aircraft were flying away from you, the red light would move and eventually disappear (it would not remain on a constant relative bearing) and there would be no risk of collision.

Since the red light remains on a constant relative bearing, the other aircraft is getting closer over time without changing its track and there is a risk of collision.

When two aircraft of the same category are converging, the aircraft that is on your right (starboard side) has priority or right-of-way and it shall maintain its heading and speed. In our example, you notice the red light to your right which means that the other aircraft has priority.

ICAO Annex 2
3.2.2 Right-of-way

3.2.2.3 Converging. When two aircraft are converging at approximately the same level, the aircraft that has the other on its right shall give way (...)