To answer part (b)

Draw lines from the circle centre "O" to "A", "B" and "C".

Label the lengths |AB| and |AC| and the lengths |OB|, |OA| and |OC|.

Consider the triangles OAB and OAC.

Are they congruent or not ?

Then try to find some internal angles in the triangles,

allowing you to find |AB|