Mass of air question with relative humidity

Sep 2016
Given data:
Volume = 425.5 m^3
Pressure = 101,700 Pa
Temp. = 294.8 Kelvin
Relative humidity = 47.8%

Question: Find the mass of the air

Now my thinking was if I take 47.8% of the volume (203.4 m^3) and plugged it into the equation

Mass = (Pressure/(Moist gas constant)x(Temp)) x (203.4)

and then do the remaining volume (dry air) in the same equation with the dry gas constant and the sum to the two values together. I have a feeling this is very wrong. I hope anyone can help me!

Thank you in advance