Can some one please help me? I don't really understand this. I'm supposed to solve for x.

Answer:
x = 17
Step-by-step explanation:
The marked angles are vertical and congruent, hence
7x + 15 = 4x + 66 ( subtract 4x from both sides )
3x + 15 = 66 ( subtract 15 from both sides )
3x = 51 ( divide both sides by 3 )
x = 17
Answer:
x = 17
Step-by-step explanation:
By the Vertical Angle Theorem, 4x+66=7x+15
4x + 66 = 7x + 15
-66 both sides
4x = 7x - 51
-7x both sides
-3x = -51
÷(-3) both sides
x = 17
x = 17