HELP! My classmates and I have been staring at this problem for two days now and it's not one from a textbook I can just look up--my prof. wrote it up. I feel like some kind of information is missing, but if you can figure it out, help would be much appreciated. The problem is as follows:

Find the average molecular weight M and specific gas constant R for some air with a water vapor pressure of 30 hPa, a total pressure of 1atm, and a temperature of 30oC.

The rest I can figure out, but we can't do the rest of the problem without solving this first part before hand!