F.2 Area of Sectors

The figure shows a plectrum(彈奏片)(a small piece of plastic which is used ofplucking of a guitar).
The plectrum is formed by a sector and two congruent right-angled triangles.
Find θ(correct your answer to the nearest degree.)

The figure :http://i194.photobucket.com/albums/z30/skywalker_handsome/aeea1bd0.jpg