Angles on one side of a straight line always add to 180°.
Look at the picture.
a = 180° - 134° = 46°
b = 180° - 130° = 50°
In a triangle, the three interior angles always add to 180°.
a + b + c = 180°
c = 180° - (46° + 50°) = 180° - 96° = 84°
x° = 180° - 84° = 96°
We can see that:
x = a + b
