Given Ms = 1.276 Msolar, and P = 4.95466 days.

a) to find the semi-major axis of the orbit, use Kepler's Third Law.
      Keep the mass in solar units, but convert the period to years.

          P = 0.013565 years


        2        1      3
       P   =   -----   a       
                Ms


       Plug in to compute a in AU.


        a  =   0.0617 AU


b) how long does it take light to travel across this orbit, from one side
      all the way to the other side?

                2 * a
         t  =   ------
                  c

  
      But we know that light takes 8.3 minutes to travel 1 AU (right?),
      so we can do this more easily as

                       a
         t  =   2 * ( ---- ) * 8.3 minutes
                      1 AU


            =   1.02  minutes