Typically on this sort of problem you'll separate the horizontal and vertical components.
Ignoring air resistance, you can solve for fall time with the equation for constant acceleration:
s = at2/2
...where a is gravitational acceleration, s is distance, and t is time. Solve for t.
...and you can figure out the car's horizontal velocity with the equation for constant velocity:
s = vt
...where v is velocity, t is the time from the calculation above, and s is the distance travelled.
Note that the equations above are simplified versions of the more general equation for Newton's second law, where some of the factors are equal to zero. The general form is:
s = s0 + v0t + at2/2
In the first equation (time for the car to fall to earth), the initial distance and initial velocity are 0, so:
s = 0 + 0t + at2/2
s = at2/2
In the second equation (horizontal distance travelled by the car), the acceleration and initial distance are 0, so:
s = 0 + v0t + 0t2/2
s = v0t
