Girl runs as 2m/s for 30 seconds, turns around and runs for 20 seconds until she reaches original spot.
2m/s x 30s = 60m, so she ran 60m forward.
60m/20s = 3m/s so she was running at a speed of 3m/s on the way back.
Average Velocity: [(2 x 30) + (-3 x 20)] / 50 = 0m/s
Average speed : [(2 x 30) + (3 x 20)] / 50 = 2.4m/s
So the answer for this question was "A".