Two parallel lines are cut by a transversal such that one interior angle is 57 (Angle 1)
The interior angle opposite to Angle 1 is
=180-57 (co-interior angles)
=123 (Angle 2)
The angle on the same straight line of Angle 1
=123 (alternate interior angles are equal)
The angle on the same straight line of Angle 2
=57 (alternate interior angles are equal)