If youknow the diameter of the circle, then
Circumference = (π) x (Diameter).
If youknow the radius of the circle, then
Circumference = (π/2) x(radius).
If you know the area of the circle, then
Circumference= 2 √ (π A) .
The closest you can get to a 2/3rds decimal is 0.66 and that goes to infinity.
It is a never ending decimal.
16 cm - 2.5 cm = 13.5 cm, which is 1/4 of the diameter of the large gear. Take 13.5 cm * 4, and you have the diameter of the large gear, which is 54 cm.