Answer:
A) 1.50x10¹² m
B) 6.13x10⁹ m
Step-by-step explanation:
A) The semi-major axis is the average of the perihelion and the aphelion distances:
where SMA: is the semi-major axis, P: is the perihelion distance and A: is the aphelion distance
So, the semi-major axis for the comet's orbit is 1.50x10¹² m.
B) To find the distance between the star and the planet at its closest approach, that is to say, at the perihelion, we need to use the Kepler's Law of orbits:
where e: is the eccentricity

Therefore, the distance from the planet to the star HATS-43 is 6.13x10⁹ m at perihelion.
I hope it helps you!