Angle at the centre of a circle by an arc
1)In the given circle, find ∠x. 
  

2)ADB is a arc of circle with centre O. If ∠ACB is 35 then ∠AOB? 
  

3)O is centre of the circle. ∠AOC is 120. Find ∠ABC. 
  

4)What describes best BA and BC. 
  

5)What does black line in circle stands for?