Thank you. I was wondering where that was. Now, can someone calculate the plane's altitude?

The shadow is about 2500 feet away. Judging from nearby houses the sun is probably about 15 degrees SouthEast of noon.

  2500 ft * sin( 15 ) = 650 ft

Someone should double-check my geometry though.

I think you need to divide by tan(15) instead, which would give 9330 ft.

Wouldn't that be the 3D distance between the shadow and the plane?

https://i.imgur.com/HWA1iZu.png

Edit: nope you're totally right. Brain fart. It's toa, not soa.