Parallel Lines Practice NO LINKS PLEASE and please explain this for me so i can understand

[tex]▪▪▪▪▪▪▪▪▪▪▪▪▪ {\huge\mathfrak{Answer}}▪▪▪▪▪▪▪▪▪▪▪▪▪▪[/tex]
In the given figure, the Angle x forms Alternate exterior angle pair with 143°, so
(since, Alternate Exterior Angles have equal measures)