10)
(n-2) x 180 = 2160
n - 2 = 12
n = 14
answer
C. 14
11)
interior angle = [(11 - 2) x 180] / 11
= (9 x 180) / 11
= 1620/11
= 147.27
exterior angle = 180 - 147.27 = 32.72
12)
heptagon has 7 sides, n = 7
interior angle = [(5 x 180)/7 = 900 / 7 = 128.57