Hello, magentarita!
Your forgot to give us the question . . .
Code:
B * * *
o *
* \ *
* \ *
\ x
* \ *
* \ *
* \ *
\ D
* o
* * \ 4
* * \
* o * - - - - - - o L
G 8
The only questions we can answer are:
. . What are the distances
amd
?
If that is indeed the question, we should know this theorem:
. . If a tangent and a secant are drawn to a circle from an external point,
. . the tangent is the mean proportional between the external segment
. . of the secant and the entire secant.
In this problem, we have: . 
Then: . 
Therefore: .
miles.