I really need some explanation cause like I’m confused

Answer:
85 ft
Step-by-step explanation:
Pythagorean Theorem:
[tex]a^{2} + b^{2} = c^{2}[/tex]
Where a and b are sides and c is the hypotenuse.
Substitute:
[tex]13^{2} + 84^{2} = c^{2}[/tex]
[tex]169 + 7,056 = c^2[/tex]
[tex]7,225 = c^2[/tex]
[tex]\sqrt{7,225} = \sqrt{c^2}[/tex]
85 = c
85 feet