This idiom is a descendant of the above. It chiefly means to go to bed (to sleep) in the sense of stopping the activity one has been doing for the night. ... The sun has set a few hours ago and we've had dinner already, so let's call it a night and restart first thing tomorrow morning
Vertical angles are congruent and therefore are equal. Just set up an equation where the two angle values are equal to one another and solve with basic algebra.
