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Explanation:
If the circumference is r = 12 cm, then the diameter is double that at d = 2*r = 2*12 = 24 cm.
This then leads to the circumference of C = pi*d = pi*24 = 24pi
This is exact in terms of pi. Replace pi with something like 3.14 to find its approximate value. The circumference is the distance around the circle's edge, aka perimeter.
