a man can row upstream at 7 k/h and downstream at 10 k/h find man's rate in still water and the rate of current

rate of still water 8.5km/h
rate of current 1.5km/h

If 'd' is the rate of speed in downstream and 'u' is the rate of speed in upstream
Rate in still water = 1/2(d+u)
Rate of current = 1/2(d-u)
Therefore, Rate in still water = 1/2(10+7) = 8.5 kmph
=> Rate of current = 1/2(10-7) = 1.5 kmph

upstream(x-y)=7kmph
downstream(x+y)=10kmph
x+y+x-y=10-7
2x=3
x=1.5kmph