Answer:
0.7 m/s
Step-by-step explanation:
velocity of first runner = 3.5 m/s
velocity of second runner = 4.20 m/s
Both the runner are running in the same direction
velocity of second runner with respect to first runner = velocity of second runner - velocity of first runner
velocity of second runner with respect to first runner = 4.20 - 3.5 = 0.7 m/s