Final answer:
The equation that represents gravitational force at a given distance from Earth's center is F.f(d) = 200 - GM / (d + 4000)^2 (option a).
Step-by-step explanation:
The equation that represents gravitational force at a distance d from Earth's center is F.f(d) = 200 - GM / (d + 4000)^2 (option a).
In this equation, F is the force, G is the gravitational constant (approximately 6.67 × 10^-11 Nm^2/kg^2), M is the mass of Earth (approximately 5.97 × 10^24 kg), and d is the distance from Earth's center in meters.
The equation accounts for the decrease in gravitational force as the distance from Earth's center increases.