A car traveling west in a straight line on a highway decreases its speed from 30.0 meters per second to 23.0 meters per second in 2.00 seconds. The Cars average acceleration during the time interval. is

Acceleration, a = (v - u) / t

Initial Velocity, u = 30 m/s

Final Velocity, v = 23 m/s

time t = 2.00 seconds

a = (23 - 30) / 2

a = - 7 / 2 = - 3.5 m/s2

So the acceleration is negative, which means it is a deceleration of 3.5 m/s2.