If the wheel does one full turn in 180 cm, that means the wheels circumference is 180. The equation for circumference is:
Circumference = (Pi) x Diameter
(Can't find the symbol for pi)
Now plug in the 180 for the Circumference:
180 = (Pi) x D
Divide by Pi:
57.296 = D
ANSWER:
The diameter is 57 cm