Answer:
C?
Explanation:
If I understand your description correctly...
Vertical Angles are angles on opposite sides of the X formed by intersecting lines, and are Congruent (equal in measure).
So, 4x-5 = x+16
4x-x-5+5 = x-x+16+5
3x = 21
3x/3 = 21/3
x = 7