Answer:
53.67kpa
Explanation:
Yeah. Honestly the most annoying part is all those pressure units. Lets convert everything to kpa.
total pressure = 96.4 kpa
1 atm = 101.3kpa
0.133 atm*(101.3kpa/1atm) = 13.47kpa = helium pressure
1mmHg = 0.133kpa
220mmHg*0.133kpa = 29.26kpa = Oxygen pressure
Now He + O2 + CH4 = total pressure
CH4 = total - O2 - He
96.4 - 29.26 - 13.47 = 53.67kpa
Hope that answers your question