First, we find the area of the circle.

However, first, we have to find the diameter of the circle, which is the hypothenuse of the right triangle.
![\begin{gathered} h^2=21^2+20^2 \\ h=\sqrt[]{441+400} \\ h=\sqrt[]{841} \\ h=29 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/qmbowvtzskjrpsuaunks3dttxbpciy9jpz.png)
So, the diameter is 29 inches long. Remember that the radius is half the diameter, 14.5 inches long. Let's find the area of the circle.

Now, we find the area of the triangle.

At last, we subtract the area of the circle and the area of the triangle to find the shaded region.

Hence, the answer is the first option.