(b) (i)
∠AOB + reflex ∠AOB = 360^o

(Angles at the point)

140^o + reflex ∠AOB = 360^o

Reflex ∠AOB = 360^o – 140^o = 220^o

Now major arc AB subtends ∠AOB + ∠OBC = 360^o

50^o + 110^o + 140^o + ∠OBC = 360⁰

300^o + ∠OBC = 360⁰

∠300^o + ∠OBC = 360⁰

∠OBC = 360^o – 300^o

∠OBC = 60^o

(ii) In Quadrilateral .OACB

∠OAC + ∠ACB + ∠AOB + ∠OBC = 360^o

50^o + 110^o + 140^o + ∠OBC = 360^o

300^o + ∠OBC = 360^o

∠OBC = 360^o – 300^o

∠OBC =60^o

(iii) in ∆OAB,

OA = OB

(Radii of the same circle)

∠OAB + ∠OBA = 180^o

2 ∠OAB = 180^o – 140^o = 40^o

∠OAB = 40^o/2 = 20⁰

But ∠OBC = 60^o

∠CBA = ∠OBC – ∠OBA

= 60^o – 20^o = 40^o