Equations of circles are typically organized in the following form:
[tex](x-h)^2+(y-k)^2=r^2[/tex]
We're given:
Plug the given information into [tex](x-h)^2+(y-k)^2=r^2[/tex]:
[tex](x-0)^2+(y-7)^2=9^2[/tex]
[tex]x^2+(y-7)^2=81[/tex]
[tex]x^2+(y-7)^2=81[/tex]