A group of astronomers measure CO emission from a cloud and
   estimate the mass of the CO to be about 20 solar masses.

   Q:  What is the mass of the molecular hydrogen in the cloud?


         The mass of a single H2 molecule is 2*mass of hydrogen atom.

         The mass of a single CO molecule is 

              (12 * mass of hydrogen atom) +  (16 * mass of hydrogen atom)

              =    28 times mass of hydrogen atom


         Therefore, each CO molecule has 14 times the mass of a single
         H2 molecule.


         To compute the mass of molecular hydrogen gas, 

                                                        1
            mass (H2)  =   mass (CO)  *  20,000   *  --------
                                                        14

                       =   mass (CO)  *   1,429

                       
                       =   about 29,000 solar masses