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.
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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) .