(i) Avg speed = Total\ Distance\over Total\ time
From, A to B
speedAB = 60 km h-1
distance travelled = dAB = d
time taken = d/60
From, B to A
speedBA = 80 km h-1
distance travelled = dBA = d
time taken = d/80
Total distance travelled = d + d = 2d
Total time = d/60 + d/80
Avg speed = 2d\over{d\over 60}+{d\over 80}
Avg speed = 2d\over{4d+3d\over 240}
Avg speed = 2d\over{7d\over 240}
Avg speed = 2 × 240\over 7
Avg speed = 480\over 7
Avg speed = 68.57 km h-1
Hence, Avg Speed = 68.57 km h-1
(ii) Average velocity = displacement\over total\ time
As the train starts from station A and comes back to same station, hence, displacement is zero.
Therefore, the average velocity is also zero.
