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
Answer:
1368
Step-by-step explanation:
I got 12.654 I'm not sure it is right though.
I'm just guessing but if you subtract the 1 from 11 and divide by 2 on both sides then T would equal 5