Answer: 51 feet
Explanation:
Hi, since the situation forms a right triangle (see attachment) we have to apply the Pythagorean Theorem:
x^2 = a^2 + b^2
Where x is the hypotenuse of the triangle (in this case length of the rope) and a and b are the other sides.
The difference between the poles' heights is equal to one side of the triangle (39-15=24), the other side of the triangle is the distance between poles (45).
Replacing with the values given:
x^2 = 24^2 + 45^2
x^2 = 576+2,025
x^2 = 2,601
x = √2,601
x = 51 feet
Feel free to ask for more if needed or if you did not understand something.