please show steps, need an understanding on how you solved it. Thank you

The main component of an oxygen supply system for an enhanced breathing unit is a pressure vessel having a volume of 50L. The vessel initially contains oxygen at a gauge pressure of 150 atm and can be used until its pressure drops to 0.2atm (gauge). The supply system is housed in a room at a constant temperature of 22C. a) [8 marks ] Assuming ideal gas behaviour, calculate the mass of oxygen (kg) that can be obtained from the pressure vessel. b) [2 marks ] Determine the validity of the ideal gas assumption used in part (a)