∠ABC= 126

∠ACB= 18

Draw auxiliary lines for the detailed process.

But if you know common sense, you don't have to draw. ∠A is 360 divided by 10, so it is 36.

The common sense of the acute angle of a pentagram is 36 degrees. If it is folded in half, it is ∠ACB, which is equal to 18.

After calculating ∠ ABC = 126 according to the triangle theorem

If you can fold the paper by yourself and cut a five-pointed star with scissors, I believe you will understand better.