[tex]\huge\boxed{\textsf{A.}\ 78.5\ \text{in}^2}[/tex]
Correction to your question text: diameter, not radius.
The area of a circle is given by:
[tex]A=\pi r^2[/tex]
The radius is half of the diameter.
[tex]A=\pi\cdot\left(\dfrac{10}{2}\right)^2[/tex]
Substitute and solve.
[tex]\begin{aligned}A&=\pi\cdot\left(\frac{10}{2}\right)^2\\&=\pi\cdot5^2\\&=\pi\cdot25\\&\approx\boxed{78.5}\end{aligned}[/tex]
