Question 297798
{{{x^2 + y^2 = 36}}}
When {{{x = 0}}}, 
{{{y = 6}}} and
{{{y = -6}}}
also
When {{{y = 0}}}
{{{x = 6}}} and
{{{x = -6}}}
So, the diameter is {{{6 - (-6) = 12}}}
measured along either axis, and the radius is
{{{12/2 = 6}}}
Just plug this into 
{{{A = pi*r^2}}}
and {{{C = 2*pi*r}}}