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.
-Determine the speed of the object after falling from rest through 16 m on this planet.

A) 28 m/s
B) 32 m/s
C) 56 m/s
D) 64 m/s
E) 320 m/s