An armada of spaceships that is 1.00ly long (in its rest frame) moves with speed 0.800c relative

Question:

An armada of spaceships that is 1.00ly long (in its rest frame) moves with speed 0.800c relative to a ground station in frame S. A messenger travels from the rear of the armada to the front with a speed of 0.950c relative to S. How long does the trip take as measured?

(a) In the messenger's rest frame,

(b) In the armada's rest frame, and