Answer:
See edit
A 20 km / hour
Step-by-step explanation:
The exact answer is 30 km / 172 which is less than 1 km / hr. Since that answer isn't offered, I suspect there is something wrong with the question. If there is a decimal after the 1 in 172 you would get 17.44 km / hr. That's roughly A.
If the decimal is not there, I think you should either resubmit the question or answer A.
Edit
The note said (below) that the ship went 30 km in 1 1/2 hours.
Rate = distance / time
distance = 30 km
time = 1 1/2 hours = 1.5 hours
rate = 30 / 1.5 = 20 km / hr
