Intial velocity(u) of the car = 20m/s
Final velocity(v) of that body = 12m/s
Time taken(t) to reduce it's spees to final velocity = 32s.
We're gonna use "Defination of acceleration" (AKA first equation of motion) here,
v = u+at
Now substitute for the values we already have,
12 = 20 + a(32)
-8 = a(32)
-8/32 =a
a = -1/4 = -0.25
Hence, acceleration here would be -0.25m/s^2
