Acceleration = (change in velocity) / (time for the change)
change in velocity = (velocity after) - (velocity before)
change in velocity = (51 m/s north) - (43 m/s south)
that's the same thing as (51 m/s north) + (43 m/s north)
change in velocity = 94 m/s north
Acceleration = (94 m/s north) / (1 second)
Acceleration = 94 m/s² north
The direction of the acceleration is North.