whats the value of x?? please help

Answer:The horizontal value in a pair of coordinates: how far along the point is. The X Coordinate is always written first in an ordered pair of coordinates (x,y), such as (12,5). In this example, the value "12" is the X Coordinate. Also called "Abscissa" See: Coordinates.
Answer:
x = 8
Step-by-step explanation:
Vertical angles are congruent.
21x-17 = 15x+31
6x-17 = 31
6x = 48
x = 8