What is the sum of interior angles in a hexagon?

##720^@## i.e. ##4pi## radians
No matter how irregular the hexagon it can always be dissected into ##4## triangles.
For example:
Each of the ##4## triangles has interior angles summing to ##180^@## – i.e. ##pi## radians.
The interior angles of the hexagon are the sum of the interior angles of the constituent triangles so sum to:
##4 * 180^@ = 720^@## or ##4pi## radians.