ok, here the formula measure of each interior angle of regular n-gon
[tex] {180}^{0} - \frac{ {360}^{0} }{n} [/tex]
octagon ~ 8-gon, so
180° - 360°/8 = 135° (A)
for the sum, we just need multiply the formula above with n
nonagon ~ 9-gon
sum = 9(180° - 360°/9)
= 9(140°) = 1260 (C)
