ANSWER:
2KM/H
Step-by-step explanation:
Time upstream: time downstream=2:1
speed is inversely proportional to time for a given distance
therefore
time upstream: time downstream =1:2
let speed upstream=x
speed downstream =2x
speed in still water =1/2(x+2x)=3x/2
3x/2=6
x=4
speed upstream =4km/h
speed downstream =2x=8km/h
rate of stream =1/2(8-4)=2km/h
HOPE IT HELPS....