If AD is tangent to the circle, then it is perpendicular to the radius OA.
Therefore, angle(DAO) = 90o.
Since there are 180o in the triangle, angle(AOD) = 180o - 90o - 28o = 62o.
Since angle(AOD) is a central angle, it has the same number of degrees as the arc it cuts off.
This means that arc(AC) has 62o.
Angle(ABC) is an inscribed angle; therefore, it has one-half of the arc that it cuts off.
Angle(ABC) = 31o.