URGENT

Av. speed = total distance travelled / total time taken

Now, let d be the distance between the stations.

then, time taken to go from A to B = d / 60 sec

and, time taken to go from B to A = d/ 80 sec

so, total time taken = (d / 60 ) + ( d / 80 )

                           

Now, Av. speed = 2 d / [ (d / 60 ) + ( d / 80 ) ]

                             = 68.57 km h^-1

Av. velocity = total displacement / total time = 0 [ as here the displacement is zero].