Ideal gas law is PV =nRT since n is constant (# moles) for this experiment, we can say PV = kT
and then P/k = T/V Pressure in the balloon is constant for all three balloons so we can say that for all three balloons P/k is constant
So initially
k = T/V =
V1/T1 = 600/285 =2.11=k for all of the balloons
Now for the second balloon ' k ' has to be the same
630/T2 =2.11 T2 = 298.6 Kelvin
For balloon 3
k = 2.11 = V3/T3 = V3/265 yields V3 = 559 ml