Given the figure ABCDEF, you can identify that it is an Irregular polygon.
As you can see, this polygon has 6 sides. Then, you can set up that:

That formula can be used to find the sum of the interior angles of a polygon.
In this case:

Then, you get:

Knowing that the sum of the interior angles of this polygon is 720°, you can set up the following equation:

Finally, solving for "x", you get:

The answer is:
