a balloon has 1.2l of a gas is at 1.1 atm.What will be the volume of the baloon if the baloon is placed in a partial vacuum with a pressure of 0.35atm?

You should be able to do this yourself.

P1V1 = P2V2
P = Pressure
V = Volume
1 denotes initial
2 denotes final

Source: Boyle's Law