Chemistry question. Gases?

You can look up the molar volume of a gas (or calculate it using pv=nrt) at any temperature and you can look up the current amospheric pressure. thus if they are equalized you know that pressure of gases in the container equal the total pressure of the system since you know the Ptotal you can use daltons law and mol fractions (to find partial pressure) or PV=nRT to find number of moles of a single sample.