Acar traveling at 25 m/s starts to decelerate steadily. it comes to a complete stop in 12 seconds. what is its acceleration?

Acceleration = (change in speed) / (time for the change)

Change in speed = (ending speed) minus (starting speed)

                            =      (0)             -      (25 m/s)     =     -25 m/s

Acceleration  =  (-25 m/s) / (12 sec)  =  -2.083 m/s²  .