Draw a figure!
The anchor point is 20 cos 50 from the base.
The first wire is attached 20 sin 50 up the tower.
The angle of inclination of the 30 m wire is given by arccos (2/3) sin 50
And the point at which the longer wire is attached is 30 sin arccos (2/3) sin 50
The distance required by the problem is the difference between the attachment points.
I seem to remember that there is an easier way to do this problem...but right off I can't remember it!