It's a Bluesky link but he use adult tags as de facto "spoiler" tags. The problem is that content is hidden if you're not logged into Bluesky. Here's a Bluesky mirror site to show the entire thread...
https://subium.com/profile/c0nc0rdance.bsky.social/post/3kpkcq2ecws22
A huge hint...
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The question asks for an approximate answer, so you can approximate the earth as a sphere. Your path will be roughly correct, since the earth’s deviation from being a sphere is extremely small, on the order of a few kilometers.