So I think I know how to solve this I just don't know what the circumference is...
The circumference of a circle is 2r(pi) so we substitue 18 for r and then put it in the calculator
(note: You could also use 3.14 as an approximation for pi and work it out yourself)
36 * pi is approximately equal to 113.1
Hope I could help!
+839 
