Angle Rules: On a Line, Around a Point, Vertically Opposite

Read how a straight line acts as a half turn. A point P sits on a horizontal line. From P, two rays head upwards, splitting the upper side of the line into three angles labelled 50, 70 and a missing angle x. The three angles together fill the upper side of the line, so 50 + 70 + x = 180. That gives x = 60 degrees. Only the angles on one side of the line are counted, never both sides at once.