Weight and G: the Weight of Spaceman Speff at the Surface

Multiple Choice

Weight and g: The weight of spaceman Speff at the surface of planet X, solely due to its gravitational pull, is 389 N. If he moves to a distance of 1.86 × 10⁴ km above the planet's surface, his weight changes to 24.31 N. What is the mass of planet X, if Speff's mass is 75.0 kg? (G = 6.67 × 10^-11 N ∙ m²/kg²)

A) 2.99 × 10²⁴ kg
B) 2.99 × 10¹⁸ kg
C) 2.99 × 10¹⁷ kg
D) 1.59 × 10¹⁸ kg