Question

A patio in the shape of a semicircle has a diameter of 21 ft.

Answer 1

The answer is 173 ft²

The area of the patio (A) is half of the area of the circle (A1) with a diameter of 21 ft:
A = A1/2

The area of the circle with radius r is: 
A1 = π * r²
π = 3.14
We do not have the radius, but we know that it is a half of the diameter:
r = 21 ft / 2 = 10.5 ft

A1 = 3.14 * (10.5)² = 346.18 ft²

So, the area of the patio is:
A = A1/2
A = 346.18 ft² / 2
A = 173.09 ft² ≈ 173 ft²