assumption:
1. all gases are at the same fixed temperature.
2. they exhibit ideal behavior.
3. no chemical reaction takes place
we can use the relation P indirectly proportional to V, ie. PV = constant.
This translates to P1V1 = P2V2
new volume of tank = V2 = 15.0L
considering nitrogen,
(35.0atm)(25.0L) = (P2)(15.0L)
partial pressure of nitrogen = P2 = (35.0atm)(25.0L) / (15.0L) = 58.3atm
considering oxygen,
(15.0atm)(10.0L) = (P2)(15.0L)
partial pressure of oxygen = P2 = (15.0atm)(10.0L) / (15.0L) = 10.0atm
total pressure in new tank = 10.0 + 58.3 = 68.3atm