The equation of the circle with center (h,k) and radius r is:
[tex](x-h)^2+(y-k)^2=r^2[/tex]In this case we have the following:
[tex]\begin{gathered} (h,k)=(3,7) \\ r=9 \\ \Rightarrow(x-3)^2+(y-7)^2=(9)^2 \end{gathered}[/tex]therefore, the equation of the circle with center (3,7) and radius 9 is:
[tex](x-3)^2+(y-7)^2=81[/tex]