To solve this problem, we will use the following diagram as reference,
Now, from the Pythagorean theorem, we know that ( we will omit the units to simplify the calculations):
[tex](r+50)^2=71^2+r^2.[/tex]Simplifying the above equation, we get:
[tex]\begin{gathered} r^2+100r+2500=71^2+r^2, \\ 100r+2500=5041. \end{gathered}[/tex]Solving the above equation for r, we get:
[tex]\begin{gathered} 100r=5041-2500, \\ r=\frac{5041-2500}{100}=25.41. \end{gathered}[/tex]Answer:
[tex]25\text{ ft.}[/tex]