Given,

ABCD is a rectangle

∠ECD = 146°

= ∠ECD+∠DCO = 180° (Linear pair of angles)

=146°+∠DCO = 180°

= ∠DCO = 180° - 146° = 34°

AND, ∠BOC = 180°- ∠OCB-∠OBC ∵ ∠OCB = ∠OBC

=∠BOC = 180°-34°-34° = 112°

∠BOC+∠AOB = 180° (Linear pair)

= 112°+ ∠AOB = 180°

= ∠AOB = 180°- 112° = 68°