I am assuming that the problem ask for the pressure in the system. To be able to calculate this, we first assume that the system acts like an ideal gas, then we can use the ideal gas equation to find for pressure P.
P V = n R T
where,
P = Pressure (unknown)
V = 0.17 m^3
n = moles of lng / methane
R = gas constant = 8.314 Pa m^3 / mol K
T = 200 K
We find for the moles of lng. Molar mass of methane = 16 kg / kmol
n = 55 kg / 16 kg / kmol
n = 3.44 kmol CH4 = 3440 mol
Substituting all the values to the ideal gas equation:
P = 3440 mol * (8.314 Pa m^3 / mol K) * 200 K / 0.17 m^3
P = 33,647,247 Pa
P = 33.6 MPa