We need to assume that air can be considered an ideal gas in this situation, otherwise the question becomes a lot more complex :-) If that is the case, we can use the law of ideal gases: P V = n R T
Let's call the initial situation "0" and the final one "1". We can apply this equation to both situations:
P0 V0 = n0 R T0
P1 V1 = n1 R T1
The question specifies that the temperature is constant, so T0 = T1. The question doesn't explicitly state that the volume is also constant, but given that this is a tank, I think it is is safe to assume that the inside volume is constant (that might not be the case any longer if the pressure is a lot higher), so V1 = V0.
What we are looking for ultimately is the ratio of n1 / n0.
If we divide the second equation by the first one:
(P1 V1) / (P0 V0) = (n1 R T1) / (n0 R T0)
Since V0 = V1 and T0 = T1, we can simplify this to:
P1 / P0 = n1 / n0
So n1 / n0 = 3.2 / 33.3 = .096 of the original air. Note that the final pressure is given with 2 significant digits, so we cannot give this fraction with better accuracy than that.
