The initial speed of the car is
V₁ = 24 m/s
Because the car comes to rest, the final speed of the car is
V₂ = 0
The distance traveled while coming to rest is
d = 90 m.
Let a = the constant acceleration.
Use the formula
V₂² = V₁² + 2ad
That is,
0 = (24 m/s)² + 2*(a m/s²)*(90 m)
Obtain
180a = -576
a = -3.4 m/s²
Because the answer is negative, the car decelerates.
Answer:
The acceleration is -3.2 m/s² (or a deceleration of 3.2 m/s²).