Explanation:
The formula for circumference when the diameter is given is C = π • d
C = circumference
π = pi
d = diameter
So to find the circumference plug in the number (18 - diameter).
C = π • 18
C = 56.5486677646
If needed to round to nearest ...
tenth = 56.5
hundredth = 56.55
However, if the directions say to use 3.14 for π (pi) then the answer would be different.
C = 3.14 • 18
C = 56.52
Hope this helps :)