15. Find the unknown angle

Let us consider the image given below and answer the question that follows.

 

 

Here, for a circle with \(O\) as the centre, area of the sector \(OAPB\) is \(\frac{9}{36}\) times the area of the circle. Find the angle subtended by '\(O\)' to form the sector.

 

The angle subtended by '\(O\)' to form the sector \(=\) \(^\circ\)