Question

Two flasks containing the same inert gas are at the same temperature and pressure of 800. mm Hg. One flask is injected into each of the flasks to allow phase equilibrium to be established. No leakage occurs. If the pressure in the 1.0 L flask is 900 mm Hg, what is the pressure in the 2.0 L flask?

Isn't phase equilibrium dependent on pressure of the vessel, not volume? If they are under the same equilibrium, the pressure has to be the same.

I may not be understanding what the situation is.

This question doesn't make sense.
Two flasks are at the same T and P "but then one is at 800 mmm Hg and the other 900 mm Hg." How can that be? Then, another, "one flask is injected into the other"---how can a flask be injected into another. Smart trick if you can do it.