The tower is 75 feet, the wire is 20 feet below the top so the wire is 55 feet above the ground.
The length of the wire is the hypotenuse of a right triangle.
Using the law of cosine:
Cos(angle) = Adjacent leg / Hypotenuse.
Cos(46) = 55 / x
X = 55/cos(46)
x = 79.2 feet