x = 100°
In a parallelogram all the interior angles must add up to 360°
Opposite angles of a parallelogram are equal
360° = x + x + 80° + 80°
360° = 2x + 160°
2x = 200°
x = 100°
Alternatively:
x and 80° are corresponding angles because they are on the same line that crosses two parallel lines. Corresponding angles are complementary and add up to 180°.
180° = x + 80°
x = 100°
