Please help me, I really need your physics help?

Question

I worked out the density of dry air by using the pressure of 994 hectapascals and the temperature of 30 degrees celcius to get the following
Rho=994×100/(287.0×303.13)=1.1426 kg/cubic metre.

Now I need to work out the mass of a pocket of air with the above conditions using the volume of 90×106 m3. You don't have to calculate it, just show me the equation I would use. Please, you're my only hope.

Answer 1

http://answers.yahoo.com/question/index;_ylt=AhPhQftSyJMcgn58FyqXLDL4xQt.?qid=20070506011025AA4wfnz