Answer:
<em>x = 9</em>
Step-by-step explanation:
Vertical angles are congruent, so their measures are equal.
4x + 6 = 7x - 21
Subtract 7x from both sides.
-3x + 6 = -21
Subtract 6 from both sides.
-3x = -27
Divide both sides by -3.
x = 9
I believe 25 has to be added as
(x*5)^2 = x^2 + 10x + 25