A mixture of He, N2, and Ar has a pressure of 23.5 atm at 28.0 °C. If the partial pressure of He is 2247 torr and that of Ar is 1329 mm Hg, what is the partial pressure of N, ? atm PN,

First I would convert atm to mm Hg like this:

23.5 atm x (760 mm/1 atm) = ? approx 18,000 but you need to use a more correct value.
Then Ptotal = pN2 + pHe + pAr = about 1800 mm
Substitute pHe and pAr and solve for pN2 in torr. If you want pN2 in atm just divide pN2 in torr by 760.
Post your work if you get stuck.