[tex]\qquad\qquad\huge\underline{{\sf Answer}}[/tex]
Concept : As we know, Angle made by an arc on the centre of the circle is double the angle made by the same arc on the part of circle.
Therefore, we can infer that :
[tex]\qquad \sf \dashrightarrow \:\angle O= 2 × \angle R[/tex]
[tex]\qquad \sf \dashrightarrow \:\measuredangle O= 2 × 28 \degree[/tex]
[tex]\qquad \sf \dashrightarrow \:\measuredangle O= 56 \degree[/tex]
I hope that helps ~
