Help me find density of air

Pressure = 14.664 psi
relative humidity = 28%
temp = 72.5 F

I know equation is like

density = P/RT, but how do I know what is the gas constant R ?

That air is a mixture and the gas laws won't work on it because of the water vapor.
If it was dry air, they could be used. The R for standard air is 53.35.
In this case a Psychrometric chart shows 0.074 lb/cu ft

v=(1/M1+(H/M2)) *RT/P

then density =1/v

M1= molecular weight of air .M1= molecular Weight of water
H=realtive humidty