​Please tell me how  to find   the angle of rotation  of the above figure, in order to find the order of rotation which is (360/∠ of rotation) 

{Please don't provide certified answer... I want only experts answer to any without providing any web link or certified answer} 

​​ Solve the following:

The order of rotational symmetry in the Fig. 12.15 given below is 

(a)  4                            (b)  8                          (c)  6                               (d) Infinitely many