The universal law of gravitation says that the gravitational force between the two masses is
F₁ = G m₁ m₂ / r ² = 6.0 × 10⁻⁶ N
where r = 12 m. When the distance between the two masses is reduced to R = 4 m, i.e. 1/3 of the original distance r, we have
F₂ = G m₁ m₂ / R ² = G m₁ m₂ / (r/3)² = 1/9 G m₁ m₂ / r ² = 1/9 F₁
so that the resulting gravitational force has 1/9 the first magnitude, or
F₂ = 1/9 (6.0 × 10⁻⁶ N) ≈ 6.7 × 10⁻⁷ N
