Let AABC be an equilateral triangle in E.G. having altitude AM= 20 where M is between C and B. If O is any point in the interior of the triangle and N, H, K are the foot of O on CB , AB, AC respectively. If ON: OH: OK = 2:3:5. Then OK= A)4 B) 6 C) 8 D)10 E)N.A.