Answer:
d)
Step-by-step explanation:
the sites of the boat alone is 16 km/h.
downstream and upstream the effective speed is then influenced plus and minus by the current.
the distance traveled is 15km.
as speed = distance/time
then distance / speed = distance / (distance/time) = time
and we know the time it takes : 5.5 hours.
so, only answer d uses the right values in the "right places".