The first thing we need to do is figure out what equation to use. We will use the following kinematic equation...
Δx = (final velocity + initial velocity) x time / 2
We know that the car accelerates from rest, so initial velocity = 0 m/s
We also know final velocity = 20 m/s and time = 12s
Now we just need to plug everything in.
Δx = (20 x 12)/2 = 120 meters