Check the picture below.
so we have two parallel lines, notice, the 115° are corresponding angles and thus equal, the 65° and 55° angles are linear angles to 115° and 125° respectively.
that leaves us with a triangle with 65° and 55°, and since all interior angles in a triangle sum up to 180°, then the last angle must be 60°, which has a twin vertical angle across the junction.
since a full revolution or a full circle go-around is 360°, the other two twin vertical angles next to the green 60° angles must be 360° - 60° - 60° = 240°, and since they're twins, each takes half of 240°.
