Acar initially traveling at 15 meters per second north accelerates to 25 meters per second north in 4 seconds.the magnitude of the average acceleration is

|Average acceleration|  =  (change in speed)  /  (time for the change) .

Change in speed = (speed at the end) - (speed at the beginning) =

                          =             (25 m/s)   -   (15 m/s)  =  10 m/s .

|Average acceleration|  =  (10 m/s) / (4 sec)  =  2.5 m/s² .

2/3=4/6 and that's 4 times 1/6. So the answer is 100% times 4 which is 400%