Answer:
86.452 m
Step-by-step explanation:
I've attached an image showing the position of the person and the string and the kite.
From the image attached, we can see that the length of the string can be calculated from pythagoras theorem since the triangle is a right angled triangle.
Thus, let length of string be denoted as s.
s = √(65² + 57²)
s = √7474
s ≈ 86.452 m