(a) 5 am on the next day
Distance covered by train A before train B leaves
Ludhiana = 60 × 3 = 180 km
Relative speed = (72 – 60) km/hr = 12 km/hr
∴ Time taken to cross each other = \(\frac{180}{12}\) hrs = 15 hrs
∴ Required time = 2 pm + 15 hrs = 5 am on the next day.