A boat is sent across a river with a velocity of 8km/h. If the resultant velocity of the boat is 10km/h, the river is flowing with a velocity of?

The boat is sent across river with velocity 8km/h with respect to river perpendicular to it. Hence →vbr=8^j
Let the velocity of river →vr=v^i
Hence the resultant velocity of boat = →vbr+→vr=√v2br+v2r
→10=√82+v2
→v=6km/h