The red arcs mean those angles are the same.
When two angles are the same the corresponding sides are also the same.
5. X = 8
6. X = 11
7. 2x-16 = 8
Add 16 to both sides:
2x = 24
Divide both sides by 2:
X = 12
8. X + 19 = 8
Subtract 19 from both sides:
X = -11