Explanation:
the sum of all angles in a quadrilateral is 360 degrees (think also about squares and rectangles with 4×90 degrees).
so, all we need to do is find the missing degrees when adding up all known angles.
i)
50 + 110 + 120 = 280
360 - 280 = 80 degrees = x
ii)
70 + 120 + 90 = 280 (when the external angle is 90 degrees, then also the internal angle is 90 degrees)
360 - 280 = 80 degrees = x