Question

An astronaut in his space suit and with a propulsion unit (empty of its gas propellant) strapped to his back has a mass of 134 kg. During a space-walk, the unit, which has been completely filled with propellant gas, ejects some gas with a velocity of +32 m/s. As a result, the astronaut recoils with a velocity of -0.32 m/s. After the gas is ejected, the mass of the astronaut (now wearing a partially empty propulsion unit) is 165 kg. What percentage of the gas propellant in the completely filled propulsion unit was depleted?