Velocity is measured by (final velocity - initial velocity)/time taken, or simply put, change in velocity/time taken. Our original velocity was 8, and our final was 22. With our information, subtract 22 by 8 and then divide by 7 (final - inital)/(time taken). 22-8 = 14 14/7 = 2. Your average acceleration was 2.0 m/s^2. The answer is D.) I hope this helps!