At atmospheric pressure, a sample of O2 gas has a volume of 55mL at 27 degrees celcius. What volume in mL will the O2 gas occupy if the temperature is decreased 0 degrees C and the pressure is held constant?

Answer 1

First, note the correct spelling of celsius.
I assume you have a typo "if the temperature is decreased TO 0.....".etc.
Use (P1V1)/T1 = (P2V2)/T2
Don't forget to change T to Kelvin.