Answer:
3.241*10âś
Explanation:
Applying Newton version of Kepler's third law;
aÂł = (Mâ + Mâ) Ă P²
where a = semimajor axis and
      P = orbital period
     Mâ = Sun's mass
     Mâ = Planet's mass
We would assume that the factor Mâ + Mâ ⥠Mâ (the mass around which the star moves in its Keplerian orbit) since the planetâs mass is so small by comparison
Therefore, Mâ = aÂł / P²
Convert light days to Astronomical Unit (AU);
5.7 light days = 173*5.7AU=986.1AU
Mâ = 986.1Âł / 17.2²
Mâ = 3.241*10âś
So the mass around which the star moves in its Keplerian orbit = 3.241*10âś