Explanation:
remember, the intersection angles of parallel lines with an intersecting line are the same at each parallel line.
and the angles on top of an intersected line and the bottom of that intersected line are also the same but left-right mirrored.
also, the sum of all angles around one point on one side of a line is 180° (because the line can be seen as a diameter of a circle, and the point as the center of that circle; so, each side of the line residents a half-circle and therefore 180°).
so, that means that the lower unmarked angle at the intersection point of the middle parallel line is also 30°.
and its supplementary angle (meaning together they have 180°) is the lower part of the large marked 250° angle.
this lower part is then
lower part° + 30° = 180°
lower part° = 180° - 30° = 150°
now we know that the upper part of that 250° angle is
upper part° + lower part° = 250°
upper part° = 250° - lower part° = 250° - 150° = 100°.
with the same principles as before we know that the unmarked supplementary angle to this upper part 100° angle is
upper part° + supplementary angle° = 180°
supplementary angle° = 180° - upper part° =
= 180° - 100° = 80°
and we know again based on the rule of the same angles at intersection points that x is then the same as this unmarked supplementary angle.
therefore, x = 80°