At a Particular Temperature the First-Order Gas-Phase Reaction 2N₂O₅ $\rarr$ 2N₂O₄ + O₂ Has a Half-Life for the Disappearance of 2N₂O₄

At a particular temperature the first-order gas-phase reaction 2N₂O₅ $\rarr$ 2N₂O₄ + O₂ has a half-life for the disappearance of dinitrogen pentoxide of 3240 s. If 1.00 atm of N₂O₅ is introduced into an evacuated 5.00 L flask, what will be the total pressure of the gases in the flask after 1.50 hours

A) 0.685 atm
B) 1.00 atm
C) 0.315 atm
D) 1.68 atm
E) 1.34 atm