If an Astronaut Whose Total Mass Is 100 Kg Ejects

If an astronaut whose total mass is 100 kg ejects 0.1 kg of gas at a speed of 50 m/s from her propulsion pistol, her recoil speed is

A) 50 m/s.
B) 5) 0 m/s.
C) 0) 5 m/s.
D) 0) 05 m/s.