If the Earth was to shrink down so as to form a black hole, what would be the black hole's (approximate) radius?

Enter your answer in millimeters.

**Details and Assumptions**:

$M_{e} = 6 \times 10^{24} \text{ kg}$.

$G = 6.67 \times 10^{-11} \text{ N m}^{2}\text{ kg}^{-2}$.

$c = 3 \times 10^{8} \text{ ms}^{-1}$.