Hello from MrBillDoesMath!
Answer:
n = 13
Discussion:
Generally for a polygon with "n" sides, the sum of the interior angles is given by (n-2)* 180. We need to solve
(n-2) * 180 = 1980 => divide both sides by 180
(n-2) = 1980/180 => as 1980/180 =11
n-2 = 11 => add 2 to both sides
n = 11 + 2 = 13
Hence the polygon has 13 sides ( and is called a "triskaidecagon"!)
Thank you,
MrB