Solution :-
Here, we have been given that lines f and g are parallel. Thus, the angle measuring 135° and ∠2 are vertically opposite angles.
And we know that vertically opposite angles measure same. Thus,
∠2 = 135°
And,
∠2 + ∠6 = 180° ( Co - interior angles sum up to 180° )
135° + ∠6 = 180°
∠6 = 180° - 135°
∠6 = 45°
Hope that helps :)