Answer:
a = 5 [m/s²]
Step-by-step explanation:
To solve this equation we must use the following equation of kinematics.

where:
Vf = final velocity = 25 [m/s]
Vo = initial velocity = 5 [m/s]
a = acceleration [m/s²]
t = time = 4 [s]
Note: The positive sign for the acceleration in the above equation means that the car is increasing its velocity.
25 = 5 +a*(4)
25 - 5 = 4*a
20 = 4*a
a = 5 [m/s²]