A boat travels 60 km upstream against the current in 5 hours

A boat travels 60 km upstream (against the current) in 5 hours. The boat travels the same distance downstream in 3 hours. What is the rate of the boat in still water

60/5=12 km/h.
60/3=20 km/h.
(20-12)/2=8/2=4 km/h is the speed of the current.
20-4=16 km/h is the speed of the boat.
12+4=16 ditto.