Answer:
3.241*10⁶
Explanation:
Applying Newton version of Kepler's third law;
a³ = (M₁ + M₂) × P²
where a = semimajor axis and
P = orbital period
M₁ = Sun's mass
M₂ = Planet's mass
We would assume that the factor M₁ + M₂ ≡ M₁ (the mass around which the star moves in its Keplerian orbit) since the planet’s mass is so small by comparison
Therefore, M₁ = a³ / P²
Convert light days to Astronomical Unit (AU);
5.7 light days = 173*5.7AU=986.1AU
M₁ = 986.1³ / 17.2²
M₁ = 3.241*10⁶
So the mass around which the star moves in its Keplerian orbit = 3.241*10⁶