hi guest!
so if 1 tower is 18m and another is 30m it would form a trapezoid, something like this:
*this is not drawn to scale*
as you can see, it forms a right triangle, with legs of 16 and 30-18=12!
so, the missing length is \(16^2+12^2=y^2\)
\(400=y^2\)
\(\boxed{y=20}\)
i hope this helped you! :)