Let's call the distance from point C to point D as "x".
We know that the distance from A to B is 8 miles, and the distance from A to D is 4 miles. To ensure that all three towers are equidistant from each other, the distance from C to B must be equal to 8 miles.
Using the Pythagorean Theorem, we can find the distance from C to D:

Expanding and simplifying the equation:



So the distance from the third tower to point D is approximately 7 miles (rounded to the nearest tenth of a mile).