A canister is approaching a 78.4 kg astronaut at 3.5 m/s in an airless spacecraft. She pushes against it, which slows it down to 1.2 m/s (but does not reverse it) and gives her a speed
of 2.4 m/s. What is the mass of this canister?

76.3 kg
55.6 kg
81.8 kg
90.0 kg