Method 1: (speed judgment method) Because x=9 m and t= 1.5 s, the average speed is obtained.

And because the initial velocity v0 = 2v = 2× 6m/s =12m/s = 43.2km/h,

As the speed exceeds 40 km/h, it can be known that the car is speeding.

Method 2: (displacement judgment method) Assuming that the car is driving at the correct speed, it stops at 1.5 s after braking, and the braking is accelerated.

Brake with this acceleration and braking displacement.

Because x ≈ 8.33 meters