Hi! :)
So the formula to find the circumference of a circle is 2
r . This formula looks hard, but i promise it's not.

is the symbol for pi, which is 3.14 in numerical form. R means the radius, which is the line from the perimeter of the circle to the center. The 2 in front of the equation just means to multiply it by two. So, first multiply 2 by 3.14 to get 6.28. Next, multiply 6.28 by the radius.
Now, i can't tell from your picture if the radius is 9.3 or 93, so here are the answers for both numbers and you can choose which is correct:
9.3*6.28=58.404
93*6.28=584.04
Hope this helps! Good luck!