The sum of all the internal angles of a hexagon is:

The general formula used to determine the sum of all internal angles of any closed polygon with $n$ sides is given by:
$$\text{Sum}=(n-2)\times 180^{\circ }$$

A hexagon is a polygon containing 6 sides, so substituting $n=6$ into our formula:

$$\text{Sum}=(6-2)\times 180^{\circ }$$

$$\text{Sum}=4\times 180^{\circ }=720^{\circ }$$