DOB is a straight line.
∴ \(\angle\)DOC + \(\angle\)COB = 180°
⇒ \(\angle\)DOC = 180° − 125° = 55°
In ∆DOC,
\(\angle\)DCO + \(\angle\)CDO + \(\angle\)DOC = 180° (The sum of the measures of the angles of a triangle is 180°)
⇒ \(\angle\)DCO + 70º + 55º = 180°
⇒ \(\angle\)DCO = 55°
It is given that ∆ODC ∼ ∆OBA.
∴ \(\angle\)OAB = \(\angle\)OCD [Corresponding angles are equal in similar triangles]
⇒ \(\angle\)OAB = 55°