if you have 12m of fencing what is the circumference
As stated, you have answered your own question. If you make
a circle with 12m of fencing, its circumference is 12m.
Did you mean to ask, "What is the diameter?" I'll answer that.
Circumference is c, diameter is d.
pi * d = c
d = c / pi
d = 12m / 3.1415
d = 3.82m
For those of us who don't live in the civilized world, that's 12.5 ft