Question is in picture

Answer:
27.5ft
Step-by-step explanation:
a² + b² = c²
Plug in what you have:
a² + 12² = 30²
Get a by itself:
a² = 30² - 12²
Simplify:
a² = 900 - 144
Simplify:
a² = 756
Simplify:
√a = √756
Then you get 27.49 and when you round you get 27.5