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