A man having a mass of 55 kg is riding a bike weighing 30 kg. There is a box with a mass of 15 kg kept on the rear seat of the bike. The man is initially riding the bike at 9.0 m/s and suddenly increases the speed to 12.0 m/s. Due to this, the box falls behind the bike. Determine the velocity of the falling box immediately after it falls off of the bike.