Answer:
36.6
Explanation:
The rule for secants is pretty simple. The product of the distance from the external point to the near intersection with the circle and the distance to the far intersection with the circle is a constant.
This means ...
... BC × AC = DC × (DC+x)
... 8 × 26 = 5 × (x +5) . . . . . AC=AB+BC = 18+8 = 26
... 208 = 5x +25 . . . . . . . . . simplify
... 183 = 5x . . . . . . . . . . . . . subtract 25
... 36.6 = x . . . . . . . . . . . . . divide by 5