The explanation/drawings offered by pqhai for this question are spot-on, so I won't rehash any of that work here. Instead, I'll focus on a 'key' element to dealing with DS questions: to get the correct answer, you have to be clear on what you KNOW and what you DON'T KNOW.
This prompt starts us off with a hexagon, which is a 'weird' shape (and is not likely to show up on Test Day). Before dealing with this shape, I'm going to start with an easier example:
If you're given a triangle, what do you really KNOW about the triangle?
1) You know it has 3 sides
2) You know that its 3 angles add up to 180 degrees
3) You know that the length of the sides are related (through the triangle inequality theorem)
4) You know that the biggest side is 'across' from the biggest angle, the smallest is across from the smallest.
What do you NOT KNOW:
1) You DON'T KNOW the lengths of the sides.
2) You DON'T KNOW the angles
3) You DON'T KNOW if it's a right triangle, isosceles, equilateral, etc.
Now, take that same perspective with this prompt. We're given a hexagon, so what do you really KNOW about it?
1) A hexagon has 6 sides
2) A hexagon has 720 degrees
What do we NOT KNOW:
1) We don't know if the sides are the same length.
2) We don't know any of the angles.
Realizing those points, working through the rest of the question isn't that tough. Most of the 'work' is really about drawing pictures and considering the various possibilities. In all DS questions, make note of the things that you don't know (and the possibilities that can occur) and you'll be better able to get to the correct answer (and have proof of it).
GMAT assassins aren't born, they're made,
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