Answer:
B, I think it's B.
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If you look closely the only difference between the two polygons is that they are a different size.
So when you divide 21 by 18 to see what fraction is being used to demonstrate the polygon I got, 7/6.
So I tried dividing 28 by 7/6 and got the answer, 24.
But since it's X + 13, I had to see which answer plus 13 would equal 24, and 11 + 13 = 24.
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Hope you have a good day, Loves!
Also if I'm right can you let me know please?