A Rock, Dropped from Rest near the Surface of an Atmosphere-Free

Multiple Choice

A rock, dropped from rest near the surface of an atmosphere-free planet, attains a speed of 20.0 m/s after falling 8.0 meters.
-How long did it take the object to fall the 8.0 meters mentioned?

A) 0.40 s
B) 0.80 s
C) 1.3 s
D) 2.5 s
E) 16 s