The formula for the sum of a polygon's angles is:
180(n-2)
n represents the number of sides of the polygon.
Let's solve for n knowing that the total of the sum of the polygon's angles is 720 degrees.
180(n-2)=720
n-2=720/180
n-2=4
n=4+2
n=6
The polygon in question has 6 sides. A polygon with 6 sides is called an hexagon.