A man runs at a speed of 4m/s to overtake a standing bus. When he is 6m behind the bus, the bus moves forward and continuous with a constant acceleration of 1.

A man runs at a speed of 4m/s to overtake a standing bus. When he is 6m behind the bus, the bus moves forward and continuous with a constant acceleration of 1.2m/s. How long does it take for him to catch up with the bus​