Step-by-step explanation:
a)
DA is tangent and at point A and OA is radius of the circle.
[tex] \therefore OA \perp DA\\
\therefore \angle OAD = 90°\\
In\: \triangle AOD\\
m\angle AOD= 180° - (m\angle OAD + m\angle ODA) \\
\therefore m\angle AOD= 180° -(90°+28°)\\
\therefore m\angle AOD= 180° -118°\\
\huge \red {\boxed {\therefore m\angle AOD=62°}} \\\\
b) \\
\because m\angle ABC = \frac{1}{2} \times m\angle AOD\\[/tex]
(Angle formed at the circumference of the circle is half the angle formed at the center of the circle)
[tex] \therefore m\angle ABC = \frac{1}{2} \times 62°\\
\huge \red {\boxed {\therefore m\angle ABC = 31°}}[/tex]
