Given is the velocity of the bus at 25 meters per second. Then it decelerates steadily. It stops after 40 seconds. To calculate for the acceleration, use this formula:
a = (vf - vo) / t
vf = 0 m/s (complete stop)
vo = 25 m/s
t = 40 s
Therefore,
a = (0 - 25) m/s / 40 s
a = - 0.625 m/s^2