Work out the interior angle of a regular polygon with 15 sides WORKING OUT PLEASE

The exterior angles of a regular polygon add up to 360°, so an exterior angle of a regular 15-sided polygon is 360/15 = 24°.

The interior angle   = 180° - exterior angle, so here, interior angle = 180° - 24° = 156°

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I would love to help....but I'm H-O-R-R-I-B-L-E with this stuff.  Sorry!