Answer:
4
Step-by-step explanation:
The product of the secant lengths to the near and far circle intersection points is the same as the square of the tangent length.
x(x +12) = (x +4)²
x² +12x = x² +8x +16 . . . . eliminate parentheses
4x = 16 . . . . . . subtract x² +8x
x = 4 . . . . . . divide by 4
