Answer:
x = 12
Step-by-step explanation:
Supplementary angles, sum = 180
10x - 20 + 6x + 8 = 180
16x - 12 = 180
16x = 192
x = 12
Simple,
writing out the problem...

Simplify it...
-4x(6+5-1)
-4x(11-1)
-4x(10)
-40x
Making it look like...

Cancel out the common factors...
Thus making the answer:

.
I would say that the angle would be an
exterior angle because it's usually between the side of the polygon connected by a line as an extension of the adjacent side.
here's an example. hope it helps!