Total amount of the interior angles of a 20 sided figure?

The number of interior angles in any polygon is the same as the number
of its sides.  So your 20-sided figure has 20 interior angles.


Wait !  Are you asking what the measures of the angles add up to ? ?

The sum of the interior angles of any polygon is

   (180 degrees) times (2 less than the number of sides).

So your 20-sided figure has interior angles that add up to

             (180 degrees) times (18) .

Hello,

The sum of interior angles of an isocagon is 18*180=3240 (°)