Consider the triangle COD. This triangle is isosceles, because OC and OD are the radii, therefore they are equal.
By the property of an isosceles triangle ∠ODC = ∠OCD = 80 °.
Consider the triangles AOW and COD. ∠DOC = ∠AOB, because they are vertical. СО = DO = OB = OA, because these are the radii of a circle.
Consequently, the triangles AOW and COD are equal (by the first sign). Therefore, ∠OBA = ∠OAB = ∠ODC = ∠OCD = 80 °
Answer: ∠OAB = 80 °.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.