The Starship Enterprise Approaches the Planet Risa at a Speed

The starship Enterprise approaches the planet Risa at a speed of 0.8c relative to the planet. On the way, it overtakes the intergalactic freighter Astra. The relative speed of the two ships as measured by the navigator on the Enterprise is 0.5c. At what speed is Astra approaching the planet?

A) 0.3c
B) 0.5c
C) 0.6c
D) 0.92c
E) 0.99c