What's the acceleration of a car that starts at rest and has a velocity of 25 m/s in 10 seconds?

Acceleration is change in velocity over change in time, a=Δv/Δt. Change in velocity is 25 m/s - 0 since the car starts from rest, change in time is 10 s, so

a= (25m/s)/(10s) = 2.5 m/s²