I'll just tell you how to do it. The area of the central (isosceles) triangle below is one-fifteenth of the area of the regular 15-gon. The base of that triangle is one-fifteenth of the perimeter of the regular 15-gon. That is,= 12 yds. The vertex angle of that isosceles triangle is one-fifteenth of 360°, or 24°. Find the area of that triangle and multiply it by 15. The green line is the height of that triangle. Edwin