[MNIO]

note sure if you have this solved yet, but how about I through in a couple of hints

this is henry's law.
  Pa = k * Ca
where
  Pa = partial pressure of component "a" over a liquid
  k = a constant (provided the temp is constant)
  Ca = concentration of component "a" in the liquid phase

you have t conditions of Pa and Ca... so what if we do this?
  Pa1 = k * Ca1
  Pa2 = k * Ca2
divide
  Pa1 / Pa2 = (k / k) * (Ca1 / Ca2)
simplify and rearrange
  Ca2 = Ca1 * (Pa2 / Pa1)

now.. that's all in partial pressures.  We don't have partial pressures, we have total pressures.  But let's make the assumption that
  Pa2 / Pa1 = Ptotal 2 / Ptotal 1
which will be close in this case
so that
  Ca2 = Ca1 * (Pa2 / Pa1)

you get to finish

[Fish200398]

I am confused. The mole of O2 is
n = PV/RT
C = n/ V water = PV/RT Vwater
C = k . P
k = C/P = n / P = V/RT V water

C2 = n2/V water = P2 V2/RT V water
C2 = k . P2 = (V/RT V water)(P2)
P2V2/RT V water = P2V/RT V water
V2 = V

Whats the poinf of henry formula? If the Volume is the same?

[Fish200398]

Ca2 = Ca1 * (Pa2 / Pa1)
n2 = n1 (P2/P1)
P2V2/RT = P1V1/RT (P2/P1)
V2 = V1

C = k P
So, this formula only for different pressure?

[Fish200398]

One of possible formulations of Henry's law is that no matter what the pressure is, the volume of the gas that dissolves in a given volume of liquid is always the same.

how about beverage drink? As it opened the pressure decrease and the gas come out(the sollubility changes?)

[Borek]

how about beverage drink? As it opened the pressure decrease and the gas come out(the sollubility changes?)

Henry's law is universal, doesn't matter if is a beverage or something else.

When you open the can or bottle pressure inside goes down, so some of the dissolved gas escapes and expands.

Note: the formulation of which I said earlier doesn't mean it is always the same amount of gas. The higher the pressure, the more gas is compressed in the same volume. It happens that number of moles in a given volume is directly proportional to the pressure, just like amount of the gas dissolved in a given volume of liquid.