A glass bulb contains air at room temperature and at a pressure of 1 atmosphere. It is placed in a chamber ﬁlled with helium gas at 1 atmosphere and at a room temperature. A few months later, the experimenter happens to read in a journal article that the particular glass of which the bulb is made is quite permeable to helium, although not to any other gases. Assuming that equilibrium has been attained by this time, what gas pressure will the experimenter measure inside the bulb when he goes back to check? Please help, the solutions manual says its 2 atmospheres but I don't really know how to start.