In a circle, chord AC is drawn. Points B and D lie on the circumference on the same side of AC. The angles ∠ABC and ∠ADC are given by 2y+10∘ and 7y−50∘ respectively.
(i) State the relationship between ∠ABC and ∠ADC, giving a suitable reason.
(ii) Find the value of y and hence the numerical value of each of these two angles.
(iii) If O is the centre of the circle, determine the measure of the central angle ∠AOC that subtends the same arc AC.