They are congruent because of the angles, which means the congruency reason should be SAS.
Using the equations for tangent and secant lines:
Let the unknown length of the line inside the circle = y
6^2 = 3 x (y+3)
Simplify:
36 = 3y+9
Subtract 9 from both sides:
27 =3y
Divide both sides by 3:
Y = 9
Now add to get x:
X = 9 + 3 = 12
X = 12
