Question

please solve it ........it's urgent

Answer 1

isolated triangle OAB
SO angle A=Angle B

Answer 2

angle ABC = 90 degree  
angle OCB=angle OBC (as Triangle OBC is an isoceles triangle as OB=OC redius)

angle OBC = 48 degree
 
angle OBA = angle ABC - angle OBC
                    = 90 - 48
                    = 42 degree

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