This means that in each triangle we have \(120^\circ\) left for the two angles lying on the side of the hexagon, so each of them is \(60^\circ\). Each interior angle (white) is two of these.

Interior angles in a quadrilateral sum to a full turn (360˚). It's possible to demonstrate and prove mathematically that the angle sum of every triangle is 180 degrees. The techniques used are ...