You need to find the new partial pressures in the container.
VT = 2 + 1 + 4 = 7 L
If no rxn occurs, and at const temp:
Pf-Hydrogen = Pi-HydrogenVi-Hydogen / VT
Pf-Oxygen = Pi-OxygenVi-Oxygen / VT
Pi-Hydrogen = 10 atm
Pi-Oxygen = 20 atm
Vi-Oxygen = 2 L
Vi-Hydrogen = 4 L
PT = Pf-Oxygen + Pf-Hydrogen
If a rxn occurs, then , I assume the water formed is in the liquid state. The reaction would be a complete one, combustion of Hydrogen. However, to find the pressures, we need to know how much Oxygen and Hydrogen are present. If the Temp is given, we can determine the number of moles and proceed to calculate the final pressure.
2H2(g) + O2(g) ---> 2H2O(l)