Answer
1km/h
Work Step by Step
The boat is moving upstream in the positive x direction at 14km/h and the water is flowing at 9km/h. Since the boat is moving upstream, it is traveling AGAINST the current, meaning that the river is flowing in the negative x direction.
Therefore, to find the speed of the boat relative to the ground we need to subtract the two (opposite directions) which would be:
14km/h (speed of boat) - 9km/h (speed of water) = 5km/h in the positive x
The child is then moving from front to rear on the boat (in the negative x direction) at 6km/h WITH RESPECT TO THE BOAT.
The boat is moving 5km/h in the positive x and the child is moving -6km/h (in the negative x direction) relative to that, which gives -1km/h for the child's speed
