Hello!
First you have to find the values that you can
Angles that are across each other are the same
So the one across 80 is 80 and the angle across 70 is 70
You know 4 of the 6 angles
You add these up together
80 + 80 + 70 + 70 = 300
All the angles together make a circle
A circle has a area of 360
So you do 360 - 300 = 60
Since there are 2 angles left you do
60/2 = 30
The answer is 30
Hope this helps!