how much will the velocty of a car be in 24 seconds

Depends on what the acceleration and initial velocity are. Here's an equation that might help with that:

Vf = Vo + at

(Where vf = final velocity, vo = initial velocity, a = acceleration, and t = time)

Assuming the car is starting from rest, this would be your equation:

Vf = (0) + a(24)
Vf = 24a