You're on a satellite orbiting an unknown planet. The only property of this planet that you know is that days are 18 hours long. Your onboard sensors show that you're orbiting at 16,000 km above the surface, with a velocity of 3 km/s. You look down and notice that you're always above the same point on that planet as you orbit around it.
Calculate the mass of the planet.

• A. 5.8×10¹⁴ kg
• B. 7.4×10²¹ kg
• C. 4.2×10²⁴ kg
• D. 6.3×10³⁴ kg