A and B are two stations, a train goes from A to B at 64

A and B are two stations, a train goes from A to B at 64 km/hr. and return to A at a slower speed. If its average speed for the whole journey is 56 km/hr. at what speed did it return ?

Let the required speed be y km/hr.
Then, ( 2 x 64 ) x [ y / (64 + y)] = 56
⇒ 128y = 64 x 56 + 56y
∴ y= (64 x 56 ) / 72
= 49.77 km/hr.