"What would the mass of air be inside a hot air balloon that has the volume of 5.25 x 10^4 L. The temperature of the air inside is 30 degrees celsius and the pressure is 95.5 kPa. Assume the composition of air is 80% nitrogen gas and 20% oxygen gas to determine the molar mass of air."

any input on how to do this would be appreciated, it's the last question on my assignment.

Similar questions that i've done like this are: What mass of oxygen, is available for a combustion reaction in a volume of 5.6L at STP

vO2 = 5.6L

vSTP = 22.4L/mol (22.4l/mol because of STP)

therefore

nO2 = 5.6 x (1mol/22.4l)

= 0.25 mol

mO2 = 0.25mol x (32.00g/1mol)

= 8 grams.

Idk how to determine the mass of the original question because it's a composition and not at STP or SATP