Hi there!
We can use the Gravitational Force equation:
[tex]F_g = \frac{Gm_1m_2}{r^2}[/tex]
Fg = Gravitational force (N)
m₁, m₂ = mass of spheres (kg)
r² = distance between the spheres
G = Gravitational Constant
We are given the force of gravity, so we can rearrange the equation to solve for r:
[tex]r^2F_g = Gm_1m_2\\\\r = \sqrt{\frac{Gm_1m_2}{F_g}}[/tex]
Plug in the given values:
[tex]r = \sqrt{\frac{(6.67*10^{-11})(2.0*10^9)(2.0*10^9)}{50}} = \boxed{231 m}[/tex]
Therefore, the correct answer is B) 231 m.