Circumference, as you noted, is represented as C = πd where d is the diameter of the circle.
The diameter is d = 2r, where r is the radius:
d = 2(1.8)
d = 3.6
You can represent the circumference in terms of π. In this case, the circumference would be 3.6π.
You can also find the exact value by substituting π for 3.14:
3.6(3.14) = 11.304
The circumference can be either 3.6π or 11.304.
