1) combined total of the degrees should be 360. Opposite angles are congruent. So if one angle is 80 so is the one opposite it. 360-160=200
Then divide by two because u need to find x which is one angle. X is 100
2) opposite sides are congruent so you set them equal.
31=2x-5
-5 -5
26=2x
/2 /2
13=x
3) you set them equal because opposite angles are congruent
x+3=4x-27
-x -x
3=3x-27
+27 +27
30=3x
/3 /3
10 = x