The sum of the angles of the five triangular shapes is 180.
The sum of the internal angles of a regular Pentagon is180 * (n-2) =180 * 3 = 540; 540/5= 108 per hour.
The triangle is an isosceles triangle, and the base angle is the outer angle of the Pentagon, that is, the base angle = 180- 108=72.
The sum of the internal angles of the triangle is 180, so the vertex angle of the triangle, that is, the vertex angle of the five-pointed star = 180-72*2=36.