Given a regular 20-gon ( a 20 sided polygon )
The measure of each interior angle will be given by:

where n is the number of sides
Substitute with n = 20
So, the measure of each interior angle =

The sum of exterior angles = 360
So, the measure of each exterior angle = 360/20 = 18
probability of you performing first is 1/13
after your team performs there are 12 teams left, so chance of the other team performing next is 1/12
chance of both happening = 1/13 * 1/12 = 1/156
Not completely sure what you are asking, but the area of a square with the side lengths of 230m would be 230*230=52,900.
The grandfather would be your parents.Hope it helps :)