Explanation:
so, we have a kite here.
a kite is a quadrilateral, that is totally symmetric along one of its diagonals.
the sum of all internal angles of a quadrilateral is always 360°.
remember, the sum of all angles around one point on one side of a line is always 180°.
a full circle airways represents 360°.
the inner angle at 140° is
180 - 140 = 40°
the inner angle at 250° is
360 - 250 = 110°
the inner angles at x and its opposing corner are equal (due to the symmetry) and are in sum with the other 2 inner angles 360°.
so, we have for the inner angles
360 = 110 + 40 + 2×xinner
210 = 2×xinner
the inner angle of x = 105°.
x (the outer angle of the inner angle of x) is
x = 360 - 105 = 255°