speed with the current=(x+y)=8 km/h
time taken=2 hours
distance=s*t=8*2=16 km
speed against current=(x-y)km/h
distance=16 km
time taken=3 hours
hence,speed=d/t=16/3 hours
x+y=8.......[1]
x-y=16/3....[2]
Adding eqns 1 and 2 we get,
2x=8+16/3
2x=(24+16)/3
2x=40/3
x=(40/3)/2
x=20/3
=6.67 km/h
Hence speed in still water=6.67 km/h