DOB is a straight line.
Therefore, ∠DOC+∠COB=180∘
⇒∠DOC=180∘−125∘=55∘
In ΔDOC,
∠DCO+∠CDO+∠DOC=180∘ (Sum of the measures of the angles in a triangle is 180∘)
⇒∠DCO+70∘+55∘=180∘
⇒∠DCO=55∘
It is given that ΔODC∼ΔOBA.
∴∠OAB=∠OCD [Corresponding angles are equal in similar triangles.]
⇒∠OAB=55∘