In given figure if angle AOB = 90 degree and angle ABC = 30 degree than find the angle CAB ???

angle AOB = 2*angle ACB (angle subtended at the centre is double the angle subtended at anywhere else on the circle)
​90  degree             = 2*Angle ACB
​45  degree            = angle AC

in triangle ACB.
Angle ACB=45 degrees
angle  CBA=30 degrees
therefore,CAB=180-(45+30)   (angle sum property of triangl)e
                        =180-75
        Angle CAB= 105 Degrees