On a long horizontally moving belt, a child runs to and fro with a speed `9 kmh^(-1)` (with respect to the belt) between his father and mother located 50 m apart on the moving belt. The belt moves with a speed of `4 kmh^(-1)`. For an observer on a stationary platform outside, what is the : speed of the child running opposite to the direction of motion of the belt.Which of the answer alter if motionis viewed by one of the parents ?