Suppose runner and cyclist reach at same position in time t, and the observer has travelled x distance in this time
Speed of runner= 15 km/h=25/6 m/s
speed of cyclist=25 km/h = 125/18 m/s
Time t = distance travelled/speed
t = (20-x)/(25/6) = (30-x)/(125/18)
x=5m
putting in equation to get t= 18/5
Speed of observer to travel 5 meter distance in 18/5 sec
=> 5/v=18/5
=> v=25/18 m/s = 5 km/h
