Explanation:
the sum of all angles around a single point on one side of a line must be 180°.
because that line can be seen as the extension of the diameter of a circle, and the point would be the center of that circle. so, one side of the line represents a half-circle, which stands for 180°.
so we have
180 = 40 + 40 + (2x + 30) = 80 + 2x + 30 = 110 + 2x
70 = 2x
x = 35