Answer:
Average acceleration = 12m/s^2
Step-by-step explanation:
Acceleration is equal to the change in velocity over the change in time:

Change in velocity is the final velocity minus the initial.
We are told the car goes from 0 to 26.8 m/s making 26.8 our final and 1 our initial. Therefore the change in velocity is 26.8-0 = 26.8m/s. (
)
And that this happens over 2.2s so this is our change in time:

Therefore our acceleration is:

Acceleration = 12.18 m/s^2
Rounded to 2 significant figures (2s.g. in 2.2s), the answer is 12m/s^2.
Hope this helped!