Initial speed of the car (u) = 15 m/s
Final speed of the car (v) = 0 m/s (Car comes to a complete stop after driver applies the brake)
Distance travelled by the car before it comes to halt (s) = 63 m
By using equation of motion, we get:

Acceleration of the car (a) = -1.78 m/s²
Magnitude of the car's acceleration (|a|) = 1.78 m/s²