$${\begin{align*}L &= \frac{4R^3}{d^2} \\&= \frac{4(2\, \mathrm{m})^3}{(4 \times 10^{-3}\, \mathrm{m})^2} \\ &= 2 \times 10^6\, \mathrm{m} \approx 10^6\, \mathrm{m} = \underline{\underline{ 10^3\, \mathrm{km}}} \end{align*}}$$