Total Distance?

Question

Let the car's initial velocity be +16.0 m/s, and the acceleration be -1.6 m/s2. What is the total distance traveled 20 s?

Neither of the following answers are correct:

0, 320, -320, 640, -640

Answer 1

d = 1/2at^2 +v0t

d = 1/2 (-1.6 m/s^2) (20 s)^2 + 16 m/s * 20 s

d = -320 + 320 = 0

Answer 2

Just set t = 20 in the equation
-1.6t^2/2 + 16t

to get the distance after 20 seconds unless the car starts to move backwards which I think it will. Then you need to solve this problem in 2 parts. First figure out the distance traveled to 0 velocity t = 16 / 1.6 = 10 seconds and then the distance traveled for the remainder of the time 20 - 10 = 10 seconds. It looks like the car will come back to the starting point so the Net distance is zero, but I think they want the distance out and back.