The equation of any given circle is:
[tex] {(x - h)}^{2}  +  {(y - k)}^{2}  =  {r}^{2} [/tex]
where (h, k) is the center and r is the radius.
In the problem, we are given the center, and the radius. When we plug them in:
[tex] {(x - 3)}^{2}  +  {(y - 7)}^{2}  = 36[/tex]
we got the formula of the circle.