So dinitrogen tetraoxide is N₂O₄ and nitrogen gas is just N₂ and Oxygen gas is O₂.
So on the left side you have 2 of nitrogens and on the right you have 2 nitrogens so that is already balanced...
But on the left you have 4 oxygens and on the right you have 2 oxygens, so you need to multiply the right oxygens by 2 to get 4 on both sides.
So overall, I believe, the balanced equation would be N₂O₄ ⇒ N₂ + 2O₂
