we know the diameter is 10, thus its radius is half that or 5.
[tex]\bf \textit{area of a circle}\\\\ A=\pi r^2~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r=5 \end{cases}\implies A=\pi 5^2\implies A=25\pi \implies \stackrel{\pi =3.14~\hfill }{A=78.5}[/tex]
