Answer
5300 m.
Work Step by Step
The subtended angle (in radians) is the spot diameter divided by the Earth to moon distance.
$$1.4 \times 10^{-5} rad=\frac{D}{3.8 \times 10^{8}m}$$
Solve for $D \approx 5300 m$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.