What have you tried with so far?
I got the pressure of O2 by calculating 741.5 - 27.1 mm Hg = 714.4 mm Hg
Then i converted it to atm so i got 0.94 atm as the pressure of O2 in atm.
I then used the PV=nRT equation to get moles ("n")
(0.94 atm)(0.8655 L) = n(0.0821 Latm/Kmol)(300.2K)
0.033 mol = n
I dont really know what to do after finding the moles !
Thanks for your help