Answer:
1620°
The formula for finding that measure is ...
sum of interior angles of n-sided convex polygon = 180°×(n -2)
For n=11, this is
sum = 180°×9 = 1620°
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Another way to get there is to remember that the sum of exterior angles is always 360° for a convex polygon. Then the total (interior + exterior) of the angles of an n-sided polygon is 180°×n. Subtracting the sum of exterior angles gives the total of interior angles: 180°×n -360° = 180°×(n -2).