Aradio station is going to construct a 5-foot tower on top of a building. the tower will be supported by three cables, each attached to the top of the tower and to points on the roof of the building that are 12 feet from the base of the tower. find the total length of the three cables

You need to use Pythagoras’ Theorem. 
A² + B² = c² and c is the hypotenuse of the right angled triangle.

The height of the tower (5 feet) is A and the distance from the end of the cable and the base of the tower (12 feet) is B. The length of ONE cable is c. So:

A² + B² = c²
5² + 12² = c²
25 + 144 = c²
169 = c²
13 = c. This is the length of one cable.

3 x 13 = 39 therefore the total length of the cables is 39 feet.

25 

The answer is option c.