The area of the cover for the hot tub must be:
38 square feet.
Here's why:
Area of a circle = pi * radius ^ 2 (you must know that the radius is half the diameter)
Then we replace the diameter:
Area of a circle = 3.14 * (3.5 feet) ^ 2
Area of a circle = 38,465 square feet. Approximately 38 square feet.