Answer:
58.9 ft²
Explanation:
The horse is constrained to 3/4 of a circle that has a 5 ft radius. Then the area is ...
A = (3/4)πr²
A = (3/4)π(5 ft)² = 75π/4 ft²
A ≈ 58.9 ft²
The horse has a maximum grazing area of 58.9 ft².
_____
In the real world, a 5 ft rope is awfully short. The grazing area would depend on how high on the barn it is tied, and where on the horse it is tied.