A bag contains five red marbles, four blue marbles, and four yellow marbles. You randomly pick a marble. What is the probability that the marble is red or blue?

n(s)= 5+4+4=13

n(e)= red + blue

=5+4

=9

so, p(e) = n(e)/n(s)

p(e)= 9/13

=0.69

it's your answer

it will help.

I'm guessing, but did you mean to ask about a regular POLYGON?
Each exterior angle of a regular POLYGON =360 degrees / (number of sides)
So for a triangle 360 / 3 = 120
a square 360 / 4 = 90
a pentagon 360 / 5 = 72
a hexagon 360 / 6 = 60
and so on.
Source:http://www.1728.org/polygon.htm