You plug in 841pi to the area equation.
841pi=pi(r)^2
You already know pi so u can take that out to find the radius.
841=r^2
r=29
Now you have the radius and can find the circumference.
Plug numbers in
C=2(pi)(29)
C=58pi
Hope this helped and sorry if I am wrong!! If you need further explanation you can ask.